Enzyme cytochemistry of rat organs after uremia with special reference to proteases

Wistar rat organs and tissues were investigated after acute and chronic uremia using enzyme cytochemical means whereby special attention was paid to plasma membrane and lysosomal proteases. Heart muscle, pancreas, spleen, stomach, duodenum, jejunum, colon and skeletal muscle did not show any clear-cut indications of alterations. After acute uremia activities of dipeptidyl peptidase IV, glutamyl aminopeptidase and microsomal alanyl aminopeptidase were decreased in the extraorbital gland and that of dipeptidyl peptidase IV in the submandibular gland. The thymus showed an increased staining for glutamyl aminopeptidase and lysosomal proteases. An activity increase of dipeptidyl peptidase IV, acid phosphatase and beta-N-acetyl-D-glucosaminidase occurred in bronchial lavage cells among which the alveolar macrophages predominated. In addition, their number was comparatively higher. Non-specific esterase activity was lowered in these cells. Alkaline phosphatase activity was drastically enhanced at the biliary pole of hepatocytes. Following chronic uremia all effects were less pronounced except for the lavage cells which were positive for glutamyl aminopeptidase, microsomal alanyl aminopeptidase and gamma-glutamyl transpeptidase and showed increased staining for lysosomal proteases, glycosidases and nonspecific phosphatases.     

A comparison of membrane enzymes of human and pig oesophagus; the pig oesophagus is a good model for studies of the gullet in man

Summary The distribution and relative catalytic activities of five plasma membrane enzymes (alkaline phosphatase, dipeptidyl peptidase IV, γ-glutamyl transpeptidase, microsomal alanyl aminopeptidase and glutamyl aminopeptidase) were examined in human and pig oesophagus. In both species, alkaline phosphatase activity occurred in basal and suprabasal cells of the epithelium and in capillaries. Stromal cells in the human submucosa were particularly reactive. Dipeptidyl peptidase IV was present in blood vessels and capillaries in man and pig and in submucous glands in the pig. The enzyme was also present in both species in the lamina propria cells immediately adjacent to the epithelial basal lamina. In the human, γ-glutamyl transpeptidase occurred in the epithelial basal cells and in isolated basal and lower prickle cells in the pig. Stromal cells in the human submucosa were strongly reactive and capillaries in the muscularis propria in both species moderately active. Microsomal alanyl aminopeptidase was detected in lamina propria cells adjacent to the epithelial basal cell layer in man and pig and at the apices of mucous cells in pig submucous glands. Weak glutamyl aminopeptidase activity was confined to capillaries in both species. The findings of this study, along with the ready availability of pig oesophagus, suggest that the pig may be a suitable model for studies of the gullet in man.     

Histochemistry of some proteases in the normal rabbit,pig and ox corneas

Summary The distribution of activities of membrane aminopeptides (aminopeptidases M (APM), aminopeptidase A (APA), dipeptidyl peptidase IV (DPP IV), -gluamyltransferase (GGT) and lysosomal exopeptidases (dipeptidyl peptidase I (DPP I), dipeptidyl peptidase II (DPP II) was investigated in rabbit, ox and pig corneas. Cryostat sections of snap-frozen corneas treated with chloroform-acetone (4°C) were used for the demonstration of membrane-bound enzymes and sections of corneas fixed in 4% paraformaldehyde (4°C) for the demonstration of lysosomal enzymes.In activities of proteases species differences were found. The rabbit cornea was most active, followed by ox and pig corneas. Individual corneal layers reacted differently. Of membrane proteases a high APM activity was found in keratocytes, whereas epithelium and endothelium were negative. On the other hand APA and GGT were active in the epithelium and endothelium. Their activities in keratocytes were less pronounced. DPP IV activity was demonstrated in some keratocytes beneath the epithelium only. Lysosomal enzymes DPP I and DPP II were active in all corneal layers. The epithelium displayed the highest activity.Differences in activities in the centro-peripheral and epithelio-endothelial directions were found. DPP I, DPP II, and APM were most active in the limbal region in all corneal layers.     

Enzymatic and morphological response of the thymus to drugs in normal and zinc-deficient pregnant rats and their fetuses

Summary In the thymus of normally fed pregnant rats the plasma membrane enzymes dipeptidyl peptidase IV (DPP IV) and alkaline phosphatase (alP) were found in cortical and medullary lymphocytes (thymocytes). Plasma membrane aminopeptidase A (APA) and adenosine monophosphate hydrolysing phosphatase (AMPP) were present in cortical reticular cells. In medullary reticular cells, aminopeptidase M (APM), -glutamyl transferase (GGT), adenosine triphosphate (ATPP) and thiamine pyrophosphate (TPPP) cleaving phosphatases were detected. Medullary reticular cells did not contain APA. Lysosomal DPP I and II, acid phosphatase, acid -d-galactosidase, -d-N-acetylglucosaminidase, -d-glucuronidase and non-specific esterases occurred especially in macrophages at the corticomedullary junction. The 21-day-old fetal thymus showed a similar reaction pattern as the maternal organ except for APA which was absent before birth.—After treatment of the pregnant rats with valproic acid (VPA), salicylic acid (SA), streptozotocin (ST) and retinoic acid (RA) APA showed an increase in activity in the thymic cortex. In addition, ST and RA induced AMPP, ATPP and TPPP activity in cortical reticular cells up to the same pattern as in medullary reticular cells. After ethanol (ET) administration severe damages occurred. The thymic cortex was free of DPP IV-positive lymphocytes; the medullary reticular cells showed reduced or no GGT and occasionally an increased APM activity. Dexamethasone (DEXA) given to normal or zinc-deficient rats produced the most severe lesions; thymocytes with DPP IV activity were completely absent in the cortex and medulla. In Zn-deficient pregnant rats similar alterations were observed as after ET. When the drugs were applied to Zn-deficient pregnant rats, the alterations resembled those observed after drug treatment alone. In all cases of severe thymus degeneration, i.e. ET and DEXA treatment and Zn-deficiency, the number of macrophages and activities of lysosomal hydrolases in macrophages and reticular cells were increased; the lysosomal hydrolases were often homogeneously distributed over the cortex. Cell contacts between reticular cells and lymphocytes were reduced. Vacuoles occurred within the reticular cells.—The fetal thymus was reduced in size and the number of macrophages and the activities of their lysosomal enzymes were increased after Zn-deficiency, DEXA treatment and Zn-deficiency combined with ET administration.Supported by the Deutsche Forschungsgemeinschaft (Sfb 174)     

Histochemistry of some proteases in the normal rabbit, pig and ox corneas

The distribution of activities of membrane aminopeptidases (aminopeptidase M (APM), aminopeptidase A (APA), dipeptidyl peptidase IV (DPP IV), gamma-glutamyltransferase (GGT) and lysosomal exopeptidases (dipeptidyl peptidase I (DPP I), dipeptidyl peptidase II (DPP II)) was investigated in rabbit, ox and pig corneas. Cryostat sections of snap-frozen corneas treated with chloroform-acetone (4 degrees C) were used for the demonstration of membrane-bound enzymes and sections of corneas fixed in 4% paraformaldehyde (4 degrees C) for the demonstration of lysosomal enzymes. In activities of proteases species differences were found. The rabbit cornea was most active, followed by ox and pig corneas. Individual corneal layers reacted differently. Of membrane proteases a high APM activity was found in keratocytes, whereas epithelium and endothelium were negative. On the other hand, APA and GGT were active in the epithelium and endothelium. Their activities in keratocytes were less pronounced. DPP IV activity was demonstrated in some keratocytes beneath the epithelium only. Lysosomal enzymes DPP I and DPP II were active in all corneal layers. The epithelium displayed the highest activity. Differences in activities in the centro-peripheral and epithelio-endothelial directions were found. DPP I, DPP II, and APM were most active in the limbal region in all corneal layers.     

Apical plasma membrane-bound enzymes of rabbit uterine epithelium

Summary In order to monitor changes in the apical cell membrane of rabbit uterine epithelium which are postulated to be a precondition for trophoblast attachment, the marker enzymes: alkaline phosphatase, aminopeptidase M, -glutamyl transferase and dipeptidyl peptidase IV were investigated during the periimplantation phase. Endometrium of early pregnancy (implantation chamber, interblastocyst endometrium; 5–8 days post coitum, d p.c.) was compared with specimens obtained at hCG-induced pseudopregnancy (p. hCG) to distinguish between membrane changes regulated by maternal plasma steroid hormones and such which might be induced locally by blastocyst-derived signals.All enzymes tested showed their main activity at 5 d p.c./p. hCG. The weakest reaction in this series of stages was generally found at 8 d p.c. (interblastocyst segments) or at 8 d p. hCG. In contrast to the rest of the epithelium, the implantation chamber retained high activity of dipeptidyl peptidase IV, and the activity of alkaline phosphatase even raised here again at 7 and 8 d p.c. indicating a direct local influence of the blastocyst on the luminal epithelium. The results suggest that 1) considerable changes occur in the composition of the apical plasma membrane of the uterine epithelium when the endometrium enters the receptive state, 2) the overall trend is towards a loss of apical-type characteristics of this membrane domain and 3) the changes are modulated both systemically (by plasma steroid hormone levels) and locally by signals from the implanting blastocyst.Abbreviations d p.c. days post coitum - d. p. hCG days post hCG injection - hCG human chorionic gonadotropin - aP alkaline phosphatase - ATPase adenosine triphosphatase - Ca²⁺-ATPase Ca²⁺-activated adenosine triphosphatase - APM aminopeptidase M - GGT -glutamyl transferase - DPP IV dipeptidyl peptidase IV - PCMB p-chloromercuric benzoate - DFP di-isopropylfluorophosphate - DMF dimethylformamide     

Peptidases in the kidney and urine of rats after castration

Summary The localization of various peptidases in the renal section of the rat was investigated histochemically, and their activities were determined fluorometrically in renal homogenate. The membrane-bound peptidases aminopeptidase A (APA), aminopeptidase M (APM), -glutamyl-transferase (-GT), dipeptidylpeptidase IV (DAP IV), and the lysosomal dipeptidyl peptidases I (DAP I) and II (DAP II) were investigated in male and female (estrus) rats both before and 30 days after castration. In addition, protein excretion and APA, APM, DAP I and DAP IV activities were measured in the urine of these animals. Histochemically, the membrane-bound peptidases are demonstrable mainly in the brush borders of the proximal tubules. In addition, APA and DAP IV are found in the glomeruli, -GT and DAP IV in the thin descending limbs of the loops of Henle, and -GT in the basal labyrinth of the S₂ and S₃ segments. The lysosomal peptidases are most concentrated in the S₁ and S₂ segments of the proximal tubule, in the distal tubule, and in certain cells of the connecting tubule and collecting duct, where they are contained in lysosomes of varying size. Sex differences and castration effects are demonstrable both histochemically and biochemically for the investigated peptidases. Histochemically these effects are most pronounced in the S₃ segments for the membrane-bound peptidases, and in the lysosomes of the proximal tubule for the lysosomal peptidases. Biochemical tests in controls show significantly higher lysosomal peptidase activities in the renal homogenate of females than of males. After castration the lysosomal peptidase activities in males increase, approaching those of females. This appears to have bearing on the sex-dependent proteinuria in rats, for lysosomal peptidases and proteinases are particularly important in the degradation of filtered proteins that are reabsorbed in the proximal tubule. In females high lysosomal peptidase activities correlate with a low proteinuria, while males demonstrate lower lysosomal peptidase activities and a significantly higher proteinuria than females. After castration, the lysosomal peptidase activities and proteinuria in males approach those in females. Renal peptidases are also excreted in the urine, again with sex differences, and so these excreted peptidases contribute to the proteinuria in rats.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)     

Proteases in the human full-term placenta

Summary Aminopeptidase A, not yet defined aminopeptidases and endopeptidases, dipeptidyl peptidase I, II and IV, -glutamyl transferase and oxytocinase were investigated in the normal human full-term placenta using qualitative (catalytic) cytochemistry, isoelectric focusing, immunocytochemistry and kinetic fluorometry. Aminopeptidase A could be visualized cytochemically in the smooth muscle cells of the chorionic plate, stem villi and basal plate blood vessels. Aminopeptidases were found in connective tissue fibres of the chorionic plate, villous stroma, basal plate and paraplacenta. Dipeptidyl peptidase IV was detected at the same sites as the aminopeptidases and, in addition, in amniotic epithelial cells, fibroblasts of the villous stroma, endothelium of chorinic plate and villous blood vessels as well as in the basophilic cytotrophoblast cells (x-cells) of the basal plate and paraplacenta, and it possibly also occurred in some domains of the plasma membrane of the syncytiotrophoblast and cytotrophoblast cells. The x-cells surrounded the fetus in the form of a dipeptidyl peptidase IV-positive shell at the border to the mother. The enzyme represented the first specific marker for x-cells. Dipeptidyl peptidase I and II were primarily found in Hofbauer cells (macrophages) of the villous stroma, but also in the syncytiotrophoblast, other villous stromal cells and cells of the chorionic and basal plate. -Glutamyl transferase was present in some connective tissue elements of the chorionic plate. Oxytocinase and endopeptidases were not detected. Isoclectric focusing of proteases revealed different molecular forms of dipeptidyl peptidase IV in the paraplacenta and villous tree, while the aminopeptidases shared the same pattern in both regions. Immunocytochemical staining of dipeptidyl peptidase IV in the villous tree resembled the pattern obtained by catalytic cytochemistry except for the blood vessel endothelium and the x-cells of the basal plate. Fluorometrically, all proteases were more active in the villous tree than in the paraplacenta. The kinetic measurements revealed the highest hydrolysis rates for dipeptidyl peptidase IV followed by the aminopeptidases. In contrast to eatalytic cytochemistry all proteases were detectable when using fluorometry.Supported by the German Research Foundation (Sfb 174)A preliminary account of this work was presented at a Symposion on Progress in General, Applied and Diagnostic Histochemistry (Smolenice, Czechoslovakia on March 24–28, 1986).     

Protease cytochemistry in the murine rodent,guinea-pig and marmoset placenta

Summary Plasma membrane and lysosomal proteases, -glutamyl transferase and extracellular matrix proteases were investigated by qualitative cytochemical means in the mature placenta of mice, rats, guinea-pigs and marmosets. These studies revealed similarities, which concerned, primarily the lysosomal proteases in different structures of the placenta and all proteases and -glutamyl transferases in the zone of placental shedding. However, species differences predominated. They were observed especially for aminopeptidase A and M, dipeptidyl peptidase IV and -glutamyl transferase in the plasma membranes and extracellular matrix of the placental barrier and decidual cells of all species and the cells of the basal zone in rats and mice. Plasma membrane and extracellular matrix proteases in other parts of the placenta, e.g. the placenta stem of guinea-pigs and basel plate, amniotic and chorionic plate of marmosets occurred only in these species. Elastase substrates hydrolysing endopeptidase I and kallikrein-, thrombin-, plasmin-, plasminogen- and cathepsin B substrates hydrolysing endopeptidase II were not observed in any of these species. A general comparison of the species revealed similarities for the mouse, rat and guinea-pig placental barrier, but not for that of marmosets. The proteases of this zone in the marmoset placenta are more similar to the human situation, but do not correspond to it completely.In honour of Prof. P. van DuijnSupported by the BMFT (Project CMT 35) and Sfb 174In part presented at a Symposion on Progress in General, Applied and Diagnostic Histochemistry (Modra, Czechoslovakia on 12–15 April, 1984; abstracts published in Histochem J 17, No 5, 1985)     

Peptidases play an important role in cataractogenesis: an immunohistochemical study on lenses derived from Shumiya cataract rats

The role of proteolytic enzymes in Shumiya cataract rats in alterations to lens proteins during cataract formation was studied immunohistochemically using antibodies against exopeptidases, such as lysosomal dipeptidyl peptidase II (DPP II), cytosolic dipeptidyl peptidase III, and soluble and membrane-bound alanyl aminopeptidases, and against cytosolic endopeptidases such as mu- and m-calpains, and 20S proteasome. AlphaB-crystallin was detected as a proteolytic marker in the lenses. A constant immunoreactivity against all the antibodies employed was observed in the lens epithelium independent of the strain and age of the rats. A weak immunoreactivity against exo- and endopeptidases and an intense reactivity against alphaB-crystallin were observed in the lens fibres of control rats at all ages. The immunoreactivity of these peptidases in lens fibres increased with age in cataract rats, but that of alphaB-crystallin decreased. No reactivity against exo- and endopeptidases was seen in the perinuclear region of lenses of control rats at all ages or in Shumiya cataract rats at 8 and 10 weeks of age, but an intense reactivity against these peptidases was observed in the lens perinuclear region of lenses in cataract rats at 12 and 14 weeks of age. AlphaB-crystallin immunoreactivity was observed with ordered striations in the lens perinuclear region of all control rats whereas the striations in this area of cataract rat lens were disorganized. Membrane-bound alanyl aminopeptidase was detected feebly in the lens epithelium and fibres of both types of rat at all weeks of age. These findings indicate that exo- and endopeptidases, except for membrane-bound alanyl aminopeptidase, are expressed intensively and are age-dependent. Conversely, the amount of alphaB-crystallin decreased with age in lens fibres of cataract rats. Calpains (mu- and m-), 20S proteasome, dipeptidyl peptidases II and III and soluble alanyl aminopeptidase are thought to induce lens opacification kinetically during cataract formation in Shumiya cataract rats through the intracellular turnover of lens proteins.     

Histochemistry of proteases in ependyma,choroid plexus and leptomeninges

Summary Aminopeptidase M (APM), aminopeptidase A (APA), dipeptidyl peptidase IV (DPP IV) and -glutamyl transferase (GGT) were demonstrated histochemically in cryostat sections of the rat brain to show the reaction pattern of ependyma, choroid plexus and leptomeninges. GGT was only demonstrable in the cell membranes of ependymal cells and in the leptomeninges; however, APA, APM and DAP IV showed a variable degree of activity in the capillary endothelium of the choroid plexus as well as in the leptomeninges. On the basis of these results, it is postulated that peptides in the cerebrospinal fluid can be cleaved extraventricularly by the enzymes demonstrated in the leptomeninges.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday     

Specific localization of membrane dipeptidase and dipeptidyl peptidase IV in secretion granules of two different pancreatic islet cells.

Endocrine cells require several protein convertases to process the precursors of hormonal peptides that they secrete. In addition to the convertases, which have a crucial role in the maturation of prohormones, many other proteases are present in endocrine cells, the roles of which are less well established. Two of these proteases, dipeptidyl peptidase IV (EC 3.4.14.5) and membrane dipeptidase (EC 3.4.13.19), have been immunocytochemically localized in the endocrine pancreas of the pig. Membrane dipeptidase was present exclusively in cells of the islet of Langerhans that were positive for the pancreatic polypeptide, whereas dipeptidyl peptidase IV was restricted to cells positive for glucagon. Both enzymes were observed in the content of secretory granules and therefore would be released into the interstitial space as the granules undergo exocytosis. At this location they could act on secretions of other islet cells. The relative concentration of dipeptidyl peptidase IV was lower in dense glucagon granules, where the immunoreactivity to glucagon was higher, and vice versa for light granules. This suggests that, in A-cells, dipeptidyl peptidase IV could be sent for degradation in the endosomal/lysosomal compartment during the process of granule maturation or could be removed from granules for continuous release into the interstitial space. The intense proteolytic activity that takes place in the endocrine pancreas could produce many potential dipeptide substrates for membrane dipeptidase. (J Histochem Cytochem 47:489-497, 1999)     

Experimental evidence for interactions between bacterial peptidase and alkaline phosphatase activity in the Baltic Sea

From the observed pattern of aminopeptidase and alkaline phosphatase activities in the Baltic Sea, the question arose whether there is an interaction between the activities of both enzymes. In experiments with 0.8 m filtered seawater, the effects of commercial alkaline phosphatase on bacterial aminopeptidase, the effects of commercial peptidase on bacterial alkaline phosphatase activity (APA), and the effects of proteins, carbohydrates and inorganic nutrients on the activities of both enzymes were investigated.Addition of commercial alkaline phosphatase stimulated bacterial aminopeptidase activity and, similarly, the addition of commercial peptidase increased the APA in bacteria. The proteins, albumin and casein, stimulated aminopeptidase activity and APA simultaneously. Experiments using ammonium and glucose suggested that stimulation of APA by peptidase could be mediated by nitrogen and carbon availability. There were also some indications that stimulation of aminopeptidase activity by alkaline phosphatase functioned by catalysing phosphate release from organic phosphorus compounds.     

Dipeptidyl peptidases in the soleus muscle of the rat before and after treatment with 5-hydroxytryptamine

Summary A moderate peptidase activity against l-lysyl-l-proline-4-methoxy--napththylamide was detected histochemically in unfixed sections of soleus muscle fibres of inbred male Wistar rats using two variants of the semipermeable membrane technique. One variant involved simultaneous coupling with tetrazotised 3,3-dimethoxybenzidine, the other post-coupling. The activity at pH 6 increased approximately three-fold in many fibres showing signs of insult in rats that had been given a single low dose of 5-hydroxytryptamine (10 mg/kg body weight) 48–72 h earlier. The hydroxytryptamine treatment was found to induce a selective myopathy. Some of the increased peptidase activity within insulted muscle fibres appeared to arise from invading mononuclear cells, but the majority seemed endogenous to muscle fibres. The peptidase activity persisted in some fibres 21–28 days after 5-hydroxytryptamine administration, by which time the whole muscle appeared histologically normal.The variation of the activity of the peptidase with pH in the presence of various inhibitors was investigated in both control and insulted muscle fibres. From its sensitivity and behaviour towards Zn²⁺, Hg²⁺, Cu²⁺, puromycin, benzethonium chloride and phenylmethylsulphonyl fluoride and its indifference towards Co²⁺, Cd²⁺; Mn²⁺ and o-phenanthroline, it is concluded that the activity can be attributed to a mixture of at least two peptidases, dipeptidyl peptidase II and an unidentified neutral dipeptidyl peptidase. The possible role of the peptidase(s) in muscle regeneration in discussed.Dedicated to Professor Dr. T.H. Schicbler on the occasion of his 65th birthday     

Lysosomal peptidases and glycosidases in rheumatoid arthritis

Lysosomal serine and cysteine proteases are reported to play a role in collagen degradation. In this study, the activities of the lysosomal cysteine proteases cathepsin B and H, dipeptidyl peptidase I, and the serine protease tripeptidyl peptidase I and dipeptidyl peptidase II, all ascribed a role in collagen digestion, were compared with those of the aspartate protease cathepsin D, and lysosomal glycosidases in leukocytes from rheumatoid arthritis patients at different stages of the disease. In all patients the activities of cysteine protease cathepsin B, dipeptidyl peptidase I, aspartate protease cathepsin D, and two glycosidases were elevated, but the activities of the serine proteases tripeptidyl peptidase I, dipeptidyl peptidase II, and the cysteine protease cathepsin H was unchanged. The magnitude of the increased activity was correlated with the duration of the disease. Patients with long-standing RA (10 years or more) had higher cysteine protease activity in their leukocytes than did those with disease of shorter duration. This tendency suggests that elevated lysosomal cysteine protease activities, together with aspartate protease cathepsin D and lysosomal glycosidases (but not serine proteases), are associated with progression of rheumatoid arthritis.     

Is there a tripeptidyl peptidase in the renal brush-border membrane?

A recent claim that the renal brush border contains a tripeptidyl peptidase [Andersen & McDonald (1987) Am. J. Physiol. 253, F649-F655] was examined. In a fluorescent assay, the hydrolysis of Gly-Pro-Met-2-naphthylamide (-NH-Nap) and Gly-Pro-Leu-NH-Nap by pig kidney microvilli was strongly inhibited by amastatin or di-isopropyl phosphorofluoridate (inhibitors of aminopeptidases and dipeptidyl peptidase IV). The products formed were shown to be Gly-Pro and Met-NH-Nap (or Leu-NH-Nap) and free 2-naphthylamine. Specific antibodies to pig and rat aminopeptidase N abolished the apparent tripeptidyl peptidase activity. We conclude that these substrates are hydrolysed by the sequential attack of dipeptidyl peptidase IV and aminopeptidase N and that pig and rat brush borders lack a detectable tripeptidyl peptidase.     

Gene cloning and biochemical characterization of eryngase,a serine aminopeptidase of Pleurotus eryngii belonging to the family S9 peptidases

Pleurotus eryngii serine aminopeptidase that has peptide bond formation activity, redesignated as eryngase, was cloned and expressed. Eryngase has a family S9 peptidase unit in the C-terminal region having a catalytic triad of Ser, Asp, and His. In the phylogenetic relations among the subfamilies of family S9 peptidase (S9A, prolyl oligopeptidase; S9B, dipeptidyl peptidase; S9C, acylaminoacyl peptidase; S9D, glutamyl endopeptidase), eryngase existed alone in the neighbor of S9C subfamily. Mutation of the active site Ser524 of the eryngase with Ala eliminated its catalytic activity. In contrast, S524C mutant maintained low catalytic activity. Investigation of aminolysis activity using l-Phe-NH₂ as a substrate showed that S524C mutant exhibited no hydrolysis reaction but synthesized a small amount of l-Phe-l-Phe-NH₂ by the catalysis of aminolysis. In contrast, wild-type eryngase hydrolyzed the product of aminolysis l-Phe-l-Phe-NH₂. Results show that the S524C mutant preferentially catalyzed aminolysis when on an l-Phe-NH₂ substrate.     

The histochemical demonstration of peptidases by natural substrates

Summary Methods for the demonstration of peptidase activities in situ using natural peptides as substrates are described and evaluated. They are based on the use of the l-amino acid oxidase of Vipera ammodytes venom (or of similar snake venom) which is able to catalyze efficiently the oxidation of Leu, Met, Phe, Ileu, Tyr, and Try set free by the action of the particular peptidase(s). Accordingly, peptides from which the mentioned aminoacids are set free can be used as substrates. Cryostat sections adherent to slides are employed which can be preextracted with chloroform-acetone mixture (, 4°C, 5 min) to eliminate lipids. All substances needed for this multistep reaction are prepared and applied in a suitable gel layer which impedes the diffusion of soluble peptidases and also of l-amino acids set free by their action. The enzyme activity is assessed from the difference between the coloration of a pair of parallel sections one of which was incubated with the substrate and the other without it.There are two possible methods: a) The method using l-amino acid oxidase-phenazonium methosulphate and NitroBT (AAO-PMS-NBT method) works in the pH range 6.5–8 and requires anaerobic conditions. The medium consists of buffered substrate, Vipera ammodytes venom, PMS, NBT and KCN and is prepared preferentially in 10% gelatine. It is allowed to set on coverslips which are picked up by slides with sections and incubated at room temperature in the dark. In addition to a quick information on the firmness of the structure association of the peptidase splitting the substrate and on the influence of the fixation on its activity the method enables its cellular localization. Microdensitometric evaluation of formazan deposition during incubation is possible (there is a linear increase in density at least up to 20 min of incubation). b) The method using l-amino acid oxidaseperoxidase-3,3-diamino benzidine hydrochloride (AAO-PO-DAB method) works in the pH range 6–9 and requires aerobic conditions. The medium consists of buffered substrate, Vipera ammodytes venom, PO and DAB and is prepared preferentially in 1% agar solution which is applied on sections either directly or as a sandwich after gelification on a slide. The incubation proceeds at 37°C. The method furnishes similar information as the preceding one, however it is less sensitive and enables histological localization only.The suitability of these methods was shown among others on the demonstration of peptidases of the gastrointestinal tract and of the arterial wall. Biochemical findings reported so far were not only confirmed but entirely new data ascertained.In the human and rat intestinal mucosa the bulk of activities directed towards dipeptides (Leu-Leu, Leu-Gly, Gly-Leu, Ser-Met) is soluble. Peptidases splitting Leu-Leu-Leu are somewhat more structure bound in the human than in the rat intestine. Activities of these peptidases which are present even in crypt enterocytes increase during the process of the differentiation of enterocytes so that enterocytes covering sites and tops of villi display the highest staining intensity. The contribution of cells of the propria to the overall activity of the mucosa of the small intestine is not decisive. As against aminopeptidases A and M, dipetidyl peptidase IV and endopeptidase enzymes splitting natural di-and tripeptides can be demonstrated also in the gastric epithelium. However, in enterocytes the corresponding activity (activities) is (are) substantially higher already in the duodenal bulb. The differences in the staining intensity between gastric epithelium and enterocytes are lower in the case when Ser-Met is used as substrate than in the case when Leu-Leu; Gly-Leu, Leu-Gly and Leu-Leu-Leu are used as substrates. In patients suffering coeliac sprue the activity of peptidases residing in enterocytes splitting the substrates given above is lower in the acute stage of the disease than in normal persons. However, these soluble peptidases seem to be affected less than the brush border peptidases (in decreasing order): endopeptidase, -glutamyl-transferase, dipeptidyl peptidase IV, aminopeptidase A and aminopeptidase M.In the human aortae the highest activity was recorded using Ser-Met and Leu-Met as substrates, followed (in the decreasing order) by Leu-Leu, Leu-Leu-Leu, Met-Met-Met, Met-Val and Ser-Leu-Leu. No activity was recorded when N-CBZ-Leu-Met was used as the substrate. In normal human aorta the highest activity resides in vasa vasorum followed by muscle cells of the media. In cells of atherosclerotic plaques the activity is usually lower, except in cells of fatty streaks and small lipoid plaques where the activity can surpass that found in other cells of the aorta.     

Lateral diffusion of luminal membrane components during secretion in parotid acinar cells of the rat

Summary The movements of the molecular components of the luminal plasma membrane during exocytotic secretion in parotid acinar cells were examined. For immunocytochemical study, we used an antiserum of dipeptidyl peptidase IV as a marker for the components of the luminal plasma membrane of acinar cells. In unstimulated acinar cells, dipeptidyl peptidase IV immunoreactivity is restricted to the luminal plasma membrane. However, after secretion was stimulated with a -adrenergic agonist, isoproterenol, immunostaining became detectable on the membrane of discharged granules. Freeze-fracture images showed that the density of intramembrane particles on the P-fracture leaflets of discharged granule membranes is much higher than that of undischarged granule membranes during secretion. These results suggest that in parotid acinar cells of the rat, the components of the luminal plasma membrane move laterally, during secretion, to the membranes of discharged granules.     

Immunoelectrophoretic studies on pig intestinal brush border proteins.

Brush borders were prepared from pig intestinal mucosa and the membrane proteins solubilized with either Triton X-100 or papain. Proteins, thus released, were used as antigens to raise antisera in rabbits. The immunoglobulin G fractions were isolated and shown by the double layer immunofluorescence staining technique to react only with the brush border region of the enterocyte. The antibodies obtained were used in immunoelectrophoretic studies on the brush border proteins. Eight hydrolytic activities were identified by the use of histo-chemical staining methods. These were the microsomal aminopeptidase (EC 3.4.11.2), aspartate aminopeptidase (EC 3.4.11.7), dipeptidyl peptidase IV (EC 3.4.14.X), lactase (EC 3.2.1.23), glucoamylase (EC 3.2.1.3), sucrase (EC 3.2.1.48), isomaltase (EC 3.2.1.10) and alkaline phosphatase (EC 3.1.3.1). In addition, at least four faint immunoprecipitates were formed but none of these were identified.