Proteolytic and Trypsin Inhibitor Activity in Germinating Jojoba Seeds (Simmondsia chinensis)

Changes in proteolytic activity (aminopeptidase, carboxypeptidase, endopeptidase) were followed during germination (imbibition through seedling development) in extracts from cotyledons of jojoba seeds (Simmondsia chinensis). After imbibition, the cotyledons contained high levels of sulfhydryl aminopeptidase activity (APA) but low levels of serine carboxypeptidase activity (CPA). CPA increased with germination through the apparent loss of a CPA inhibitor substance in the seed. Curves showing changes in endopeptidase activity (EPA) assayed at pH 4, 5, 6, 7, and 8 during germination were distinctly different. EPA at pH 4, 5, 6, and 7 showed characteristics of sulfhydryl enzymes while activity at pH 8 was probably due to a serine type enzyme. EPA at pH 6 was inhibited early in germination by one or more substances in the seed. Activities at pH 5 and later at pH 6 were the highest of all EPA throughout germination and increases in these activities were associated with a rapid loss of protein from the cotyledons of the developing seedling.     

Partial characterization of a protease inhibitor which inhibits the major endopeptidase present in the cotyledons of mung beans

Germination of mung beans (Phaseolus aureus, Roxb.) is accompanied by an increase in the activity of the endopeptidase involved in storage protein metabolism. Enzyme activity in the cotyledons increases 25-fold during the first 5 days of germination. The cotyledons also contain inhibitory activity against the endopeptidase, and this inhibitory activity declines during germination, suggesting that inhibitors may play a role in regulating the activity of the endopeptidase.     

Trypsin inhibitor in mung bean cotyledons: purification, characteristics, subcellular localization, and metabolism

Trypsin inhibitor was purified to homogeneity from seeds of the mung bean (Vigna radiata [L.] Wilczek). The protease inhibitor has the following properties: inhibitory activity toward trypsin, but not toward chymotrypsin; isoelectric point at pH 5.05; molecular weight of 11,000 to 12,000 (sodium dodecyl sulfate gel electrophoresis) or 14,000 (gel filtration); immunological cross-reactivity against extracts of black gram and black-eyed pea, but not against soybean; no inhibitory activity against vicilin peptidohydrolase, the principal endopeptidase in the cotyledons of mung bean seedlings.

The trypsin inhibitor content of the cotyledons declines in the course of seedling growth and the presence of an inactivating factor can be demonstrated by incubating crude extracts in the presence of β-mercaptoethanol. This inactivating factor may be a protease as vicilin peptidohydrolase rapidly inactivates the trypsin inhibitor. Removal of trypsin inhibitory activity from crude extracts by means of a trypsin affinity column does not result in an enhancement of protease activity in the extracts.

The intracellular localization of trypsin inhibitor was determined by fractionation of crude extracts on isopycnic sucrose gradients and by cytochemistry with fluorescent antibodies. Both methods indicate that trypsin inhibitor is associated with the cytoplasm and not with the protein bodies where reserve protein hydrolysis occurs. No convincing evidence was obtained which indicates that the catabolism of trypsin inhibitor during germination and seedling growth is causally related to the onset of reserve protein breakdown.

     

A Bacterial Indole-3-acetyl-L-aspartic Acid Hydrolase Inhibits Mung Bean (Vigna radiata L.) Seed Germination Through Arginine-rich Intracellular Delivery

Indole-3-acetyl-L-aspartic acid (IAA-Asp) is a natural product in many plant species and plays many important roles in auxin metabolism and plant physiology. IAA-Asp hydrolysis activity is, therefore, believed to affect plant physiology through changes in IAA metabolism in plants. We applied a newly discovered technique, arginine-rich intracellular delivery (AID), to deliver a bacterial IAA-Asp hydrolase into cells of mung bean (Vigna radiata) seeds and measured its effects on mung bean seed germination. IAA-Asp hydrolase inhibited seed germination about 12 h after the enzyme was delivered into cells of mung bean seeds both covalently and noncovalently. Mung bean seed germination was delayed by 36 h when the enzyme protein was noncovalently attached to the AID peptide and longer than 60 h when the enzyme protein was covalently attached to the AID peptide. Root elongation of mung bean plants was inhibited as much as 90% or 80%, respectively, when the IAA-Asp hydrolase was delivered with the AID peptide by covalent or noncovalent association. Further thin-layer chromatography analysis of plant extracts indicated that the levels of IAA increased about 12 h after treatment and reached their peak at 24 h. This result suggests that IAA-Asp hydrolase may increase IAA levels and inhibit seed germination of mung bean plants and that the AID peptide is a new, rapid, and efficient experimental tool to study the in vivo activity of enzymes of interest in plant cells.     

Entamoeba histolytica and E. invadens: sulfhydryl-dependent proteolytic activity

Sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME) activated proteolytic enzymes present in extracts of Entamoeba histolytica and E. invadens; SDS (0.5%) and 2-ME (1.4 and 715 mM) doubled the enzymatic activity when assayed on a stained insoluble substrate. Urea (4 M) did not reduce this activity, suggesting that amebic proteases are stable in the above denaturant conditions. Specific reagents for sulfhydryl (-SH) groups completely inhibited proteolytic activity regardless of pH. Inhibition with alkylating agents, such as N-ethylmaleimide and iodoacetamide, was reversed with 715 mM 2-ME as was also observed with papain. We conclude from these results that the main proteolytic enzymes contained in extracts of E. histolytica and E. invadens are dependent on free thiol groups.     

Entamoeba histolytica and E. invadens: Sulfhydryl-Dependent Proteolytic Activity1

Sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME) activated proteolytic enzymes present in extracts of Entamoeba histolytica and E. invadens; SDS (0.5%) and 2-ME (1.4 and 715 mM) doubled the enzymatic activity when assayed on a stained insoluble substrate. Urea (4 M) did not reduce this activity, suggesting that amebic proteases are stable in the above denaturant conditions. Specific reagents for sulfhydryl (-SH) groups completely inhibited proteolytic activity regardless of pH. Inhibition with alkylating agents, such as N-ethylmaleimide and iodoacetamide, was reversed with 715 mM 2-ME as was also observed with papain. We conclude from these results that the main proteolytic enzymes contained in extracts of E. histolytica and E. invadens are dependent on free thiol groups.     

Characterization of asparaginyl endopeptidase activity in endosperm of developing and germinating castor oil seeds

A spectrophotometric assay was devised to characterize the asparaginyl (Asn) endopeptidase activity from the endosperm of castor oil seeds. (Ricinus communis L. var. Baker 296). The assay measures the release of p-nitroaniline from the hydrolysis of benzoyl-l-Asn-p-nitroanilide. Assay sensitivity was improved through diazotization of the reaction product with N(]-napthy])-ethylenediamine dihydrochloride: diazotized p-nitroaniline was determined spectrophotometrically at 548 nm (?₅₄₈= 1.64 × 10^?1M^?1 cm^?2). By using this assay. Asn endopeptidase activity was detected in endosperm extracts of developing, mature and germinating castor seeds. Comparison of the Asn endopeptidase activities of developing and germinating castor endosperms revealed that they: 1) have identical pH-activity profiles with optimal activity occuring at pH 5.4: 2) are heat-labile proteins displaying comparable thermal stability profiles, and 3) are activated and inhibited by dithiothreitol and thiol modifying reagents, respectively. Thus, the Asn endopeptidases of developing and germinating castor seeds are very similar, if not identical, cysteine proteases. The most significant increase in the activity of endosperm Asn endopeptidase occurs during the full coryledon to maturation stage of seed development, this period coincides with the most active phase of reserve protein accumulation by ripening castor oil seeds. Asn endopeptidase activity of fully mature (dry) castor seeds was about 2-fold lower than that of muturation stage ripening castor oil seed. Asn endopeptidase activity showed a slight reduction over the inicial 2-day period following seed imbibition, and then rapidly decreased over the next several days of germination. The results are compatible with the proposal that Asn endopeptidase functions both to process storage preproteins following their import into protein bodies of developing seeds, as well as to participate in the mobilization of storage proteins during the early phase of seed germination.     

Histochemical and biochemical observations on storage protein metabolism and protein body autolysis in cotyledons of germinating mung beans

Storage protein hydrolysis in the cotyledons of germinating mung beans (Phaseolus aureus Roxb.) was examined by histochemical techniques, and the autolytic capacity of isolated protein bodies was studied with biochemical methods. The localization of endopeptidase activity within the cotyledons was studied using an India ink-gelatin film technique. After 24 hours of imbibition, a low level of endopeptidase activity was found throughout the storage tissues of the cotyledons. A marked increase in activity was noted in cells farthest from the vascular bundles 48 to 60 hours after the start of imbibition. The decrease in storage protein followed the same spatial distribution starting in the cells farthest from the bundles. The cotyledons contain a population of cells in various stages of endopeptidase activity enhancement and storage protein degradation. A wave of endopeptidase activity moves progressively through the cotyledons towards the vascular bundles leaving behind areas devoid of stored reserves and low in endopeptidase activity. Observations on the morphology of protein bodies during germination indicate that the membrane surrounding them remains intact, while the reserves disappear. This result suggests that the protein bodies may be undergoing autolysis. To determine whether this may indeed be the case, protein bodies were isolated from the meal of mung bean seeds using an aqueous medium containing 80% glycerol. The protein body preparations and the cytoplasm were assayed for the presence of a number of enzymes which may be involved in the breakdown of the storage proteins. The protein bodies contained all, or nearly all, of the carboxypeptidase, α-mannosidase, N-acetyl-β-glucosaminidase, and caseolytic activity. The cytoplasm contained all, or most, of the leucine aminopeptidase and the trypsin-like activity (benzoyl arginine-p-nitroanalide as substrate). Incubation of the isolated protein bodies resulted in the release of amino acids. An analysis of the products of hydrolysis indicated that very little, if any, storage protein was being hydrolyzed during the incubation. Hydrolysis of the storage proteins present in the protein bodies was greatly accelerated by the addition of extracts from the cotyledons of 4-day-old seedlings. The results suggest that new enzymic activities not present in the protein bodies isolated from dry seeds must either be activated or synthesized and possibly added to the protein bodies before storage protein breakdown can begin.     

Neutral peptidases in the stroma of pea chloroplasts

One endopeptidase (EP1) and at least three aminopeptidases (AP1, AP2, and AP3) were discovered in the stroma of chloroplasts isolated from pea seedlings (Pisum sativum L.), and purified over 100-fold. EP1 requires added Mg²⁺ or Ca²⁺ for activity, may have an additional tightly bound metal atom, and is inhibited by sulfhydryl reagents but not by serine residue-directed inhibitors. It is reversibly inhibited by dithiothreitol. Its specificity is for the bond between two adjacent Ala or Gly residues. Its molecular mass is 93 kilodaltons, estimated on a gel filtration column. Aminopeptidase activities were detected with the aid of different amino acyl-β-naphthylamides as substrates. They were resolved into at least three individual proteins by gel filtration and DEAE-cellulose chromatography, having apparent molecular masses of 269,000 (AP1), 84,000 (AP2), and 42,000 (AP3) daltons, respectively. Each has a unique specificity for substrates, with AP1 hydrolyzing only the Prolyl-β-naphthylamide. None of the APs require added divalent cations for activity, but the possibility of a tightly bound metal function was suggested in AP2 and AP3 (not AP1) from effects of inhibitors. A probable sulfhydryl residue function was indicated for all three, from inhibition by p-hydroxymercuribenzoate and Zn²⁺. All these peptidases had pH optima at 7.7.     

An Assessment of Proteolytic Enzymes in Tetrahymena thermophila

Cellular extracts of Tetrahymena thermophila were found to contain substantial levels of proteolytic activity. Protein digestion occurred over broad ranges of pH, ionic strength, and temperature and was stimulated by treatment with thiol reductants, EDTA and sodium dodecyl sulfate. Incubation at temperatures ≥60° C or with high concentrations of chaotropic reagents such as 10 M urea or 6 M guanidine-HCl caused an apparent irreversible loss of activity. Activity was also strongly diminished by increasing concentrations of divalent cations. Several peptide aldehydes, p-hydroxymercuribenzoate, and alkylating reagents such as iodoacetate, N-tosyl-L-lysine chloromethyl ketone, N-tosyl-L-phenylalanine chloromethyl ketone, N-methylmaleimide, and trans-epoxysuccinyl-L-leucylamido-(4-guanidino)-butane were potent inhibitors of proteolytic activity. Aprotinin diminished activity by approximately 40% while benzamidine, 3,4-dichloroisocoumarin, and trypsin inhibitors from soy bean, lima bean, and chicken egg caused relatively modest inhibition of proteolytic activity. Phenylmethanesulfonyl fluoride had no apparent effect. Electrophoretic separation of proteins on SDS-polyacrylamide gels copolymerized with gelatin substrate revealed that at least eight active proteolytic enzymes were present in cell extracts ranging in apparent molecular weight from 45,000 to 110,000. Five of these apparent proteases were detected in 70% ammonium sulfate precipitates. Gelatinase activity was not detectable when extracts were pretreated with iodoacetate or E-64, indicating that all of the enzymes observed in activity gels were sensitive to thiol alkylation. Cellular extracts of T. thermophila appeared to contain multiple forms of proteolytic enzymes which were stimulated by thiol reductants and inhibited by thiol modifying reagents. Accordingly, the proteolytic enzymes present in cell extracts appear to be predominantly cysteine proteinases.     

Patterns of proteolytic enzyme activities in different tissues of germinating corn (Zea mays L.)

Profiles of pH dependence and activities of live proteolytic enzymes, amino- and carboxypeptidase and endopeptidases active at pH 3.8, 5.4 and 7.5, with casein as substrate, were determined in crude extracts from the various organs of corn seedlings during germination and early development (30°C, dark, 8 d). With respect to the endopeptidases, caseolytic activities at pH 3.8, 5.4 and 7.5 in extracts from endosperm increased concurrently with loss of endosperm N during germination; however, the relative amounts of the pH 7.5 activity were very small. In scutellum extracts, caseolytic activities at both pH 5.4 and 7.5 increased during the initial stages of development but only the increase at pH 5.4 was concurrent with loss of scutellar N. In shoot extracts, caseolytic activities at pH 5.4 and 7.5 were very low and remained relatively constant. There was a progressive increase in shoot N with time. In root extracts, caseolytic activities at pH 5.4 and 7.5 were higher (3-fold) than in shoot extracts. The activity at pH 5.4 remained constant while the activity at pH 7.5 increased during germination. The rate of accumulation of N by the root was low after day 5. The pattern and ratio but not the amounts of the pH 5.4 and 7.5 caseolytic activities of the root were similar to those observed in senescing leaves of field-grown corn. Addition of mercaptoethanol increased (several-fold) the caseolytic activities at pH 3.8 and 5.4, especially the latter, but not the pH 7.5 activity in endosperm extracts and increased the pH 5.4 activity in extracts from scutellum (30%) and roots (30%) while the effect in shoot extracts was negligible. Carboxypeptidase activity was relatively low in young tissue (root tip, 3-d-old shoots) and increased with development of the various organs except the roots (whole) where the activity remained relatively constant. The increases in carboxypeptidase activities were concurrent with decreases in N from endosperm and scutellum; this result indicates that this enzyme in these tissues may be involved (cooperatively with endopeptidases) in the mobilization of reserve protein.Of all the enzymes tested, only carboxypeptidase activity was markedly (in excess of 50%) inhibited by phenylmethylsulfonylfluoride. Only aminopeptidase activity was found in appreciable amounts in endosperm and scutellum of dry kernels. Aminopeptidase activity was highest in organs with high metabolic activity (scutella, shoot, root tips) and decreased in plant parts undergoing rapid loss of nitrogen (endosperm, senescing leaves).Abbreviations AP aminopeptidase - CA caseolytic activity - CP carboxypeptidase - ME mercaptoethanol     

An assessment of proteolytic enzymes in Tetrahymena thermophila.

Cellular extracts of Tetrahymena thermophila were found to contain substantial levels of proteolytic activity. Protein digestion occurred over broad ranges of pH, ionic strength, and temperature and was stimulated by treatment with thiol reductants, EDTA and sodium dodecyl sulfate. Incubation at temperatures > or = 60 degrees C or with high concentrations of chaotropic reagents such as 10 M urea or 6 M guanidine-HCl caused an apparent irreversible loss of activity. Activity was also strongly diminished by increasing concentrations of divalent cations. Several peptide aldehydes, p-hydroxymercuribenzoate, and alkylating reagents such as iodoacetate, N-tosyl-L-lysine chloromethyl ketone, N-tosyl-L-phenylalanine chloromethyl ketone, N-methylmaleimide, and trans-epoxysuccinyl-L-leucylamido-(4-guanidino)-butane were potent inhibitors of proteolytic activity. Aprotinin diminished activity by approximately 40% while benzamidine, 3,4-dichlorosocoumarin, and trypsin inhibitors from soy bean, lima bean, and chicken egg caused relatively modest inhibition of proteolytic activity. Phenylmethanesulfonyl fluoride had no apparent effect. Electrophoretic separation of proteins on SDS-polyacrylamide gels copolymerized with gelatin substrate revealed that at least eight active proteolytic enzymes were present in cell extracts ranging in apparent molecular weight from 45,000 to 110,000. Five of these apparent proteases were detected in 70% ammonium sulfate precipitates. Gelatinase activity was not detectable when extracts were pretreated with iodoacetate or E-64, indicating that all of the enzymes observed in activity gels were sensitive to thiol alkylation. Cellular extracts of T. thermophila appeared to contain multiple forms of proteolytic enzymes which were stimulated by thiol reductants and inhibited by thiol modifying reagents. Accordingly, the proteolytic enzymes present in cell extracts appear to be predominantly cysteine proteinases.     

Protease II from Escherichia coli. Purification and characterization.

We have previously demonstrated the existence of two types of endopeptidase in Escherichia coli. A purification procedure is described for one of these, designated protease II. It has been purified about 13,500-fold with a recovery of 24%. The isolated enzyme appears homogeneous by electrophoresis and gel filtration. Its molecular weight is estimated by three different methods to be about 58,000. Its optimal pH is around 8. Protease II activity is unaffected by chelating agents and sulfhydryl reagents. Amidase and proteolytic activities are stimulated by calcium ion, which decreases the enzyme stability. Like pancreatic trypsin, this endopeptidase catalyses the hydrolysis of alpha-amino-substituted lysine and arginine esters. It appears distinct from the previously isolated protease I, which is a chymotrypsin-like enzyme. The apparent Michaelis constant for hydrolysis of N-benzoyl-L-arginine ethyl ester is 4.7 X 10(-4) M. The esterase activity is inhibited by diisopryopylphosphorofluoridate (Ki(app) equals 2.7 X 10(-3) M) and tosyl lysine chloromethyl ketone (Ki(app) equals 1.8 X 10(-5) M), indicating that serine and histidine residues may be present in the active site. However, protease II is insensitive to phenylmethanesulfonyl fluoride and several natural trypsin inhibitors. Its amidase and esterase activities are competitively inhibited by free arginine and aromatic amidines. The proteolytic activity measured on axocasein is very low. In contrast to trypsin, protease II is without effect on native beta-galactosidase. It easily degrades aspartokinase I and III. Nevertheless both enzymes are resistant to proteolysis in the presence of their respective allosteric effectors. These results provide further evidence that such differences in protease susceptibility can be related to the conformational state of the substrate. The possible implication of structural changes in the mechanism of preferential proteolysis in vivo, is discussed.     

Changes in the Activity of Some Hydrolases, Peroxidase, and Catalase in the Rice Seed during Germination

A study was made of the changes in activity of enzymes involved in the breakdown of stored phytin, lipid, and hemicellulose in the aleurone layer of rice seed (Oryza sativa L., variety IR8) during the 1st week of germination in the light. Enzyme assays were made on crude extracts from degermed seed, and activities were expressed on a per seed basis. Phytase activity increased within the 1st day of germination. The increase in activity of most other enzymes—phosphomonoesterase, phosphodiesterase, esterase, lipase, peroxidase, catalase, β-glucosidase, and α- and β-galactosidase—closely followed the increase in protein content. Their peak activities occurred by the 5th to the 7th day. Some enzymes, such as β-1, 3-glucanase and α-amylase, continued to increase in activity after the 7th day. Phytase, β-1, 3-glucanase, and α-amylase followed a similar sequence of production in embryoless seed halves incubated in 0.12 μM gibberellin A₃, but the production of lipase was delayed.     

Hemoglobin-digesting Acid Proteinases in Soybean Leaves: CHARACTERISTICS AND CHANGES DURING LEAF MATURATION AND SENESCENCE

Three proteinases which digest hemoglobin rapidly at acid pH (3.5 to 4.5) were identified in crude extracts of soybean (Merr.) leaves and separated by chromatography on DEAE-cellulose. All three enzymes were endopeptidases as judged by the ratio of α-amino-nitrogen plus peptide nitrogen over α-amino-nitrogen in the trichloroacetic acid-soluble portion of hemoglobin digests. Proteinase I did not bind to diethylaminoethyl cellulose and was not inhibited by any of the proteinase inhibitors tested. Proteinase II was partially inhibited by phenylmethylsulfonyl fluoride, N-ethylmaleimide, and p-chloromercuribenzoate. The inhibition by phenyl-methylsulfonyl fluoride can probably be accounted for by the presence of contaminating carboxypeptidase. Proteinase III was the most anionic of the three and required the presence of sulfhydryl reagents to prevent the irreversible loss of activity. All the proteinase preparations digested soy-bean ribulose bisphosphate carboxylase as shown by the disappearance of the large subunit of that protein, when partially digested preparations were subjected to electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. These experiments confirmed that the three proteinases were endopeptidases. All three proteinases were present throughout leaf development; proteinase I predominated in expanding leaves, whereas proteinase III became the predominant enzyme as the leaves matured. Senescence (yellowing) was associated with a decline in the activities of all three proteinases.     

Enzymic mechanism of starch breakdown in germinating rice seeds I. An analytical study

Time-sequence analyses of carbohydrate breakdown in germinating rice seeds shows that a rapid breakdown of starch reserve in endosperm starts after about 4 days of germination. Although the major soluble carbohydrate in the dry seed is sucrose, a marked increase in the production of glucose and maltooligosaccharides accompanies the breakdown of starch. Maltotriose was found to constitute the greatest portion of the oligosaccharides throughout the germination stage. α-Amylase activities were found to parallel the pattern of starch breakdown. Assays for phosphorylase activity showed that this enzyme may account for much smaller amounts of starch breakdown per grain, as compared to the amounts hydrolyzed by α-amylase. There was a transient decline in the content of sucrose in the initial 4 days of seed germination, followed by the gradual increase in later germination stages. During the entire germination stage, sucrose synthetase activity was not detected in the endosperm, although appreciable enzyme activity was present in the growing shoot tissues as well as in the frozen rice seeds harvested at the mid-milky stage. We propose the predominant formation of glucose from starch reserves in the endosperm by the action of α-amylase and accompanying hydrolytic enzyme(s) and that this sugar is eventually mobilized to the growing tissues, shoots or roots.     

In Vitro Stability and Inactivation of Peptide Hydrolases Extracted from Phaseolus vulgaris L.

Endopeptidase activity against azocasein had a higher temperatureoptimum (50°C) in leaf extracts than in cotyledon extracts(37°C). The temperature optima for aminopeptidase (46°C)and for carboxypeptidase (53°C) were similar in leaf andcotyledon extracts. The endopeptidase activity showed an excellentstability in crude extracts from leaves even at 37°C, whilethe endopeptidase in cotyledon extracts was less stable. Carboxypeptidasewas very stable in both leaf and cotyledon extracts. Aminopeptidasewas the least stable of the enzymes investigated and its inactivationrate depended on the source of the extract. A moderate stabilitywas observed in extracts of leaves or of ungerminated seeds,but this enzyme was rapidly inactivated in cotyledon extractsat pH 5.4. At pH 7.5 aminopeptidase remained active longer thanat pH 5.4. From experiments with mixed extracts it could beconcluded that in cotyledons an aminopeptidase inactivatingfactor was formed during germination. This factor was heat sensitive,excluded by Sephadex G-25, precipitated by 75% ammonium sulfateand inhibited by tosyl-L-lysine chloromethyl ketone. These datasuggest that the factor is a protein and considering the similarproperties it appears possible that it is the endopeptidaseformed during germination. (Received May 15, 1981; Accepted July 18, 1981)     

Superoxide dismutase undergoes proteolysis and fragmentation following oxidative modification and inactivation

Red blood cells (RBC) are thought to be well protected against oxidative stress by the antioxidant, cu-pro-zinc enzyme superoxide dismutase (CuZn SOD) which dismutates O2- to H2O2. CuZn SOD, however, is irreversibly inactivated by its product H2O2. Exposure of intact RBC to H2O2 resulted in the inactivation (up to 50%) of endogenous SOD in a concentration-dependent manner. When RBC were exposed to O2- and H2O2, generated by xanthine + xanthine oxidase, an even greater loss of SOD activity (approximately 75%) was observed. Intracellular proteolysis was markedly increased by exposure to these same oxidants; up to a 12-fold increase with H2O2 and a 50-fold increase with xanthine oxidase plus xanthine. When purified SOD was treated with H2O2, inactivation of the enzyme also occurred in a concentration-dependent manner. Accompanying the loss of SOD activity, the binding of the copper ligand to the active site of the enzyme diminished with H2O2 exposure, as evidenced by an increase in accessible copper. Significant direct fragmentation of SOD was evident only under conditions of prolonged exposure (20 h) to relatively high concentrations of H2O2. Gel electrophoresis studies indicated that under most experimental conditions (i.e. 1-h incubation) H2O2, O2-, and H2O2 + O2- treated SOD experienced charge changes and partial denaturation, rather than fragmentation. The proteolytic susceptibility of H2O2-modified SOD, during subsequent incubation with (rabbit, bovine or human) red cell extracts also increased as a function of pretreatment with H2O2. Both enzyme inactivation and altered copper binding appeared to precede the increase in proteolytic susceptibility (whether measured as an effect of H2O2 concentration or as a function of the duration of H2O2 exposure). These results suggest that SOD inactivation and modification of copper binding are prerequisites for increased protein degradation. Proteolytic susceptibility was further enhanced by H2O2 exposure under alkaline conditions, suggesting that the hydroperoxide anion is the damaging species rather than H2O2 itself. In RBC extracts, the proteolysis of H2O2-modified SOD was inhibited by sulfhydryl reagents, serine reagents, transition metal chelators, and ATP; suggesting the existence of an ATP-independent proteolytic pathway of sulfhydryl, serine, and metalloproteases, and peptidases. The proteolytic activity was conserved in a "Fraction II" of both human and rabbit RBC, and was purified from rabbit reticulocytes and erythrocytes to a 670-kDa proteinase complex, for which we have suggested the trivial name macroxyproteinase. In erythrocytes macroxyproteinase may prevent the accumulation of H2O2-modified SOD.(ABSTRACT TRUNCATED AT 400 WORDS)     

Preparation of an exopeptidase-enriched fraction from the hepatopancreas of decapods

A laboratory-scale process suitable for the large-scale recovery of exopeptidases from the hepatopancreas tissue of decapod viscera is described. A method for distinguishing the relative exopeptidase and endopeptidase activities of digestive proteases was developed and used to monitor the enrichment of exopeptidases in an endo- and exopeptidase mixture. Simple extracts of the digestive tissues from decapods were a rich source of proteolytic activity; however, they contain a relatively high ratio of endopeptidase to exopeptidase activity. Based on the finding that most of the endopeptidase activity of extracts was inhibited by serine proteinase inhibitors, the relative exopeptidase activity of crayfish and langostilla crab digestive proteases was enriched by Agarose-SBTI affinity chromatography.     

Purification and properties of two proteolytic enzymes with carboxypeptidase activity in germinated wheat

Two proteolytic enzymes with carboxypeptidase activity have been isolated from a germinated wheat extract and partially characterized. Both enzymes rapidly released amino acids from hemoglobin and gluten and hydrolyzed carbobenzoxy-phenylalanylalanine. The enzymes were inhibited by diisopropylphosphofluoridate, but unaffected by salts, ethylenediaminetetraacetate, and sulfhydryl reagents at lower concentrations, and had molecular weights of approximately 55,000 and 61,000. Analysis of the hydrolysis products of hemoglobin and gluten indicated that both enzymes had broad specificities, including the ability to release proline.