Molecular weight and subunit size of fatty acid synthetase from rabbit mammary gland.

Fatty acid synthetase purified from the mammary gland of the rabbit has a mol. wt. of 968000 as determined by gel filtration. The enzyme gave one band, corresponding to a mol.wt. of approx. 35000, on polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate and phenylmethanesulphonyl fluoride.     

Functional polarity of the rat hepatocyte surface membrane. Isolation and characterization of plasma-membrane subfractions from the blood-sinusoidal, bile-Canalicular and contiguous surfaces of the hepatocyte.

1. Six rat liver plasma-membrane subfractions of different density and morphological, enzymic and chemical properties were prepared from homogenates by a combination of differential, rate-zonal and density-gradient centrifugation. They consisted of three vesicular 'light' subfractions of density 1.12-1.13 and three 'heavy' subfractions of density 1.16-1.18 containing membrane strips and intercellular junctions. 2. All six subfractions contained a basal adenylate cyclase activity. One of the 'light' subfractions that showed the highest glucagon-stimulated adenylate cyclase activity was identified as deriving form the blood-sinusoidal face of the hepatocyte. This subfraction, unlike the others, was contaminated by Golgi components, as indicated by its morphological properties and the presence of galactosyl- and sialyl-transferase activities. 3. All the six subfractions showed high activities of the following plasma-membrane marker enzymes: 5'-nucleotidase, alkaline phosphodiesterase (nucleotide pyrophosphatase), alkaline phosphatase, leucine naphthylamidase and Mg2+-activated adenosine triphosphatase. A 'light' subfraction that showed the highest specific activities of all the above marker enzymes, but lacked a glucagon-stimulated adenylate cyclase activity, was identified as deriving from the bile-canalicular face of the hepatocyte. 4. The 'heavy' subfractions, which showed generally the lowest activities of the above plasma-membrane enzyme markers, and were characterized by the presence of desmosomes and gap junctions, were taken to originate from the contiguous faces of the hepatocyte. 5. The protein composition of the six subfractions was generally similar, as shown by polyacrylamide-gel electrophoresis. Differences in the amounts of various protein and glycoprotein bands among the subfractions correlated with their morphology, enzymic composition and sialic acid content. 6. Hormonal and histochemical evidence supporting the identification of a bile-canalicular subfraction, a blood-sinusoidal subfraction and contiguous-face subfractions is discussed.     

Resolution of rat mitochondrial matrix proteins by two-dimensional polyacrylamide gel electrophoresis.

The mitochondrial matrix subfractions from rat liver, kidney cortex, brain, heart, and skeletal muscle were isolated and their protein components were resolved by two-dimensional polyacrylamide gel electrophoresis, revealing between 120 and 150 components for each matrix subfraction. Excellent resolution was obtained utilizing a pH 5 to 8 gradient in the first dimension and in 8 to 13% exponential acrylamide gradient in the second dimension, increasing the number of mitochondrial matrix proteins observed 3-fold over one-dimensional systems. Protein components tentatively identified by co-migration with pure enzymes and by known tissue distributions are carbamoyl-phosphate synthetase (EC 2.7.2.5), ornithine transcarbamylase (EC 2.1.3.3), glutamate dehydrogenase (EC 1.4.1.3), pyruvate carboxylase (EC 6.4.1.1), citrate synthase (EC 4.1.3.7), fumarase (EC 4.2.1.2), aconitase (EC 4.2.1.3), alpha-ketoglutarate dehydrogenase (EC 1.2.4.2), dihydrolipoyl transsuccinylase (EC 2.3.1.12), lipoamide dehydrogenase (EC 1.6.4.3), glutamate-aspartate aminotransferase (EC 2.6.1.1), and the two subunits of pyruvate dehydrogenase (EC 1.2.4.1). Protein components unambiguously identified by peptide mapping are citrate synthase, aconitase, and pyruvate carboxylase. The inner membrane subfraction from rat liver mitochondria was also resolved two dimensionally; the alpha and beta subunits of ATPase (F1) (EC 3.6.1.3) were identified by peptide mapping.     

Secretion granules of the rabbit parotid gland. Isolation, subfractionation, and characterization of the membrane and content subfractions.

A fraction of secretion granules has been isolated from rabbit parotid by a procedure which was found to be especially effective in reducing contamination resulting from aggregation and/or cosedimentation of granules with other cell particulates. The fraction, representing 15 percent (on the average) of the total tissue amylase activity, was homogeneous as judged by electron microscopy and contaminated to exceedingly low levels by other cellular organelles as judged by marker enzymatic and chemical assays. Lysis of the granules was achieved by their gradual exposure to hypotonic NaHCO3, containing 0.5 mM EDTA. The content and the membranes separated by centrifugation of the granule lysate were characterized primarily by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis which indicated that the content was composed of a limited number of molecular weight classes of polypeptides of which three bands (having approximate mol wt 58,000, 33, 000, and 12,000) could be considered major components. The gel profile of the membrane subfraction was characterized by 20-30 Coomassie brilliant blue-staining bands of which a single species of mol wt 40,000 was the conspicuous major polypeptide. Two types of experiments employing gel electrophoretic analysis were carried out for identifying and assessing the extent of residual secretory protein adsorbed to purified granule membranes: (a) examination of staining and radioactivity profiles after mixing of radioactive secretion granule extract with nonradioactively labeled granule membranes and (b) comparison of gel profiles of secretion granule extract and granule membranes with those of unlysed secretion granules and secretory protein dischraged from lobules in vitro or collected by cannulation of parotid ducts, the last two samples being considered physiologic secretory standards. The results indicated that the membranes were contaminated to a substantial degree by residual, poorly extractable secretory protein even though assays of membrane fractions for a typical secretory enzyme activity (amylase) indicated quite through separation of membranes and content. Hence, detailed examination of membrane subfractions for residual content species by gel electrophoresis points to the general unity and sensitivity of this technique as a means for accurately detecting a defined set of polypeptides occurring as contaminants in cellular fractions or organelle subfractions.     

Muscle D-glyceraldehyde-3-phosphate dehydrogenase from Anas sp.--1. Purification and properties of the enzyme

Muscle D-GPDH from Anas sp. ws isolated and purified. Basic kinetic constants and physico-chemical studies are reported. The enzyme is a tetramer with a mol. wt of 140,000. Sodium dodecyl sulfate polyacrylamide gel electrophoresis gave s single band with a mol. wt of approx. 36,000. The other catalytic properties of the enzyme are discussed relative to those of enzyme obtained from other sources.     

Alanine aminotransferase and some other enzymes in different populations of free brain cortex mitochondria

The activity of certain key enzymes involved in glutamic acid metabolism was studied in purified brain mitochondria and in mitochondrial subfractions separated in a discontinuous 1.2--1.6 mol/l sucrose gradient. Alanine aminotransferase and glutamate dehydrogenase were found to be matrix enzymes and aspartate aminotransferase to be associated with the inner mitochondrial membranes. After the purified mitochondria had been separated into 5 subfractions, aspartate aminotransferase and NAD+-dependent isocitrate dehydrogenase were found to be bound to the lighter mitochondrial subfractions settling at the 1.4--1.5 mol/l sucrose boundary while alanine aminotransferase, 4-aminobutyrate transaminase and glutamate dehydrogenase were associated with the heavier subfractions settling below 2.4 mol/l sucrose. The highest specific activity of the given enzymes was found in the subfraction settling at the 1.4--1.5 mol/l sucrose boundary, the only exception being alanine aminotransferase activity, whose maximum was found in the subfractions settling in 1.5 and 1.6 mol/l sucrose. It was concluded that alanine aminotransferase, in conjunction with glutamate dehydrogenase, is linked to NH3 binding and to the oxidation of reduced adenine nucleotides; in addition, alanine aminotransferase is presumed to have the function of transporting glutamate from the mitochondria to the extramitochondrial space.     

Some molecular properties of NAD(P)H dehydrogenase from rat liver

NAD(P)H dehydrogenase (EC 1.6.99.2) purified from rat liver cytosol revealed three discrete bands, of mol.wts. about 27000, 18000 and 9000, when subjected to polyacrylamidegel electrophoresis in the presence of sodium dodecyl sulphate. Elution of the bands from the gel and individual re-electrophoresis on separate gels showed that the 27000-mol.wt. band yielded three bands similar to those obtained with the intact enzyme, whereas the 18000-mol.wt. band retained its characteristic mobility. Amino acid analysis of native enzyme and protein extracted from each of the three bands from sodium dodecyl sulphate/polyacrylamide gels suggests that the native enzyme is composed of two subunits and that each subunit consists of two dissimilar non-covalently bound polypeptides, so that altogether the enzyme is composed of four polypeptides, two of mol.wt. 18000 and two of mol.wt. 9000. NAD(P)H dehydrogenase was active over a wide pH range with no sharp optimum. The same K(m) value for NADH but different values for V(max.) were obtained for the enzyme purified from Sprague-Dawley and Wistar rats. In immunodiffusion, however, the enzymes from the two rat strains showed a reaction of complete identity. NAD(P)H dehydrogenase was effectively inhibited by thiol-blocking reagents, indicating that the activity is dependent on free thiol group(s). By amino acid analysis six cysteine residues were found per mol of enzyme. Guanidino-group- and amino-group-selective reagents had only moderate inactivating effects on the enzyme activity.     

Subfractionation of hepatic endosomes in Nycodenz gradients and by free-flow electrophoresis. Separation of ligand-transporting and receptor-enriched membranes.

The complexity of rat liver endosome fractions containing internalized radioiodinated asialotransferrin, asialo-(alkaline phosphatase), insulin and prolactin was investigated by using free-flow electrophoresis and isopycnic centrifugation in Nycodenz gradients. Two subfractions were separated by free-flow electrophoresis. Both subfractions contained receptors for asialoglycoprotein and insulin. Glycosyltransferase activities were associated with the more electronegative vesicles, whereas 5'-nucleotidase and alkaline phosphodiesterase activities were associated with the less electronegative vesicles. Three subfractions were separated on Nycodenz gradients. Two subfractions, previously shown to become acidified in vitro, contained the ligands. At short intervals after uptake (1-2 min), ligands were mainly in subfraction DN-2 (density 1.115 g/cm3), but movement into subfraction DN-1 (density 1.090 g/cm3) had occurred 10-15 min after internalization. Low amounts of glycosyltransferase activities were associated with subfraction DN-2, and 5'-nucleotidase and alkaline phosphodiesterase activities were mainly located in subfraction DN-1. The binding sites for asialoglycoproteins and insulin were distributed towards the higher density range in the Nycodenz gradients, thus indicating a segregation of receptor-enriched vesicles and those vesicles containing the various ligands 10-15 min after internalization. Electron microscopy of the subfractions separated on Nycodenz gradients indicated that whereas the ligand-transporting fractions consisted mainly of empty vesicles (average diameter 100-150 nm), the receptor-enriched component was more granular and smaller (average diameter 70-95 nm). The properties of the endosome subfraction are used to assign their origin to the regions of the endocytic compartment where ligand-receptor dissociation and separation occur.     

The interrelations between high- and low-molecular-weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase

Galactocerebrosidase (β-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000±34000 and 121000±10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000±22000 (mean±s.d.) and 256000±12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues.     

The composition and proposed subunit structure of egg-white beta-ovomucin. The isolation of an unreduced soluble ovomucin.

1. New preparations of reduced carboxymethylated beta-ovomucin (S-carboxymethyl-beta-ovomucin) were homogeneous by sedimentation analysis, analytical sedimentation to equilibrium in CsCl gradients, and disc electrophoresis in sodium dodecyl sulphate. 2. Degradation of S-carboxymethyl-beta-ovomucin with either CNBr or trypsin indicated the presence of a subunit (approx. mol. wt. 112300). 3. Electron microscopy showed that S-carboxymethyl-beta-ovomucin consisted of chains of globular units (approx. mol. wt. 103 000). IN 6M-guanidinium chloride S-carboxymethyl-beta-ovomucin existed mainly as an aggregate (mol. wt. 720 000). 4. S-Carboxymethyl-beta-ovomucin contained ester sulphate (4.24%, W/W) and carbohydrate (60%, W/W), which consisted of large amounts of galactose (22%, W/W), galactosamine (8.9%, W/W) and sialic acid (10.6%, W/W). 5. An unreduced soluble fibrous component (component SGH) extracted from crude ovomucin precipitate with 5M-guanidinium chloride contained beta-ovomucin (approx. 70%, W/W). By using the Scheraga-Mandelkern equation the molecular weight of component SGH was calculated to be 11.5 times 10(6).     

The covalent nature of the human antithrombin III--thrombin bond.

1. Cleavage of the human antithrombin III--thrombin complex with [14C]methoxyamine hydrochloride results in inactive thrombin and 14C-labelled antithrombin III. 2. Discontinuous polyacrylamide-gel electrophoresis of the reduced dissociation fragments of the complex in the presence of sodium dodecyl sulphate reveals two antithrombin III bands that do not resolve during electrophoresis without reduction. The heavy band has the electrophoretic mobility of the native protein. The light band has an apparent mol.wt. that is approx. 4000 less than the molecular weight of native antithrombin III. 3. Treatment of the cleavage products of the complex with carboxypeptidase B yields 1 mumol of arginine, a new C-terminal amino acid, per mumol of thrombin dissociated. The results indicate that during formation of the antithrombin III--thrombin complex, the inhibitor is cleaved at an arginine--X bond; this arginine residue forms a carboxylic ester with the enzyme, while the excised polypeptide remains bound through a disulphide bridge(s).     

Studies on the assembly of the rat lens capsule. Biosynthesis and partial characterization of the collagenous components.

1. Isolated rat lens capsules synthesized hydroxy[3H]proline-containing polypeptides when incubated with [3H]proline. 2. The collagenous polypeptides synthesized during a 2 h incubation were analyzed by both gel-filtration chromatography and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and shown to have an apparent mol.wt. of approx. 180,000. 3. No evidence was obtained for conversion of these polypeptides into a lower-molecular-weight species in experiments where capsules were labelled for 2 h and chased with non-radioactive proline for up to 22 h. However, a time-dependent incorporation of the 180,000-mol.wt. species into a larger collagenous component was observed and this could be prevented by the inclusion of beta-aminopropionitrile in the incubation medium. 4. The radioactive components synthesized by the capsules correspond to subunits of the intact lens capsule and the direct incorporation of the polypeptide of mol.wt. 180,000 into deoxycholate-insoluble basement membrane was demonstrated.     

Purification of the enzyme NADPH: protochlorophyllide oxidoreductase.

A procedure for the purification of the enzyme NADPH:protochlorophyllide oxidoreductase is described. This involves fractionation of sonicated oat etioplast membranes by discontinuous-sucrose-density-gradient centrifugation, which gives membranes in which the enzyme is present at a high specific activity. The enzyme is solubilized from the membranes with Triton X-100, followed by gel filtration of the extract; enzyme activity is eluted in fractions corresponding to a mol.wt of approx. 35000. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of the enzyme-containing fractions from gel filtration shows two peptides, of mol.wts. approx. 35000 and 37000.     

Identification of immunodominant Trypanosoma musculi antigens recognized by monoclonal antibody and curative immunoglobulin G2a antibody.

Trypanosoma musculi obtained from normal or irradiated (900 rad) hosts or from in vitro cultures were lysed and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Similar protein banding patterns with a molecular weight (mol. wt) range from 34 to 68 kDa were observed between the two bloodstream forms. In comparison, lysates of cultured parasites showed a unique banding pattern of antigens within the same mol. wt range. Western blot of bloodstream form lysates, probed with immune plasma (IP), revealed a wide range of parasite proteins. However, when probed with the IgG2a-enriched fraction of IP, a major band of approximately 66 kDa was detected on the blot. Several bands of higher mol. wt were also observed. When anti-T. musculi monoclonal antibodies were used to probe the blot, the 66 kDa protein was again recognized. Using indirect fluorescence, live bloodstream form parasites were analysed by flow cytometry and the p66 protein was determined to be a surface molecule. Finally, lysates of 35S-methionine-labelled trypanosomes were immunoprecipitated with Sepharose linked anti-T. musculi monoclonal antibodies and the eluted ligand analysed by SDS-PAGE and autoradiographed. The 66 kDa band was identified, therefore confirming that this protein was of parasite origin.     

A novel 40S multi-snRNP complex isolated from rat liver nuclei.

Two structurally distinct RNP complexes (MI and MII), each with a sedimentation value of approx. 40S, were isolated from rat liver nuclear extracts by sucrose gradient centrifugation and subsequent native gel electrophoresis of the 40S hnRNP-containing fractions. MII RNP contained the bulk of hnRNA and hnRNP proteins (i.e. the 32-45KD core proteins and polypeptides of 60-80 and 110-130KD). MI RNP was characterized by the exclusive presence of U-snRNAs (U1, U2, U4, U5 and U6), their well known snRNP polypeptides and a number of Sm-associated proteins in the range of 50-210KD. Immunoselection experiments employing a monoclonal antibody with an established specificity for the U2-snRNP-specific B" polypeptide proved that the RNA and protein components characteristic of MI were part of a single multi-snRNP unit. The prominent 200/210KD protein doublet of MI was identified immunochemically as the rat homologue of the yeast PRP8 protein, a known U5-associated splicing component. Based on the major biochemical and immunochemical features of MI and MII RNP complexes, we conclude that MII represents the monomeric 40S hnRNP structure, whereas MI defines a novel multi-snRNP entity.     

The structure and mechanism of stem bromelain. Evaluation of the homogeneity of purified stem bromelain, determination of the molecular weight and kinetic analysis of the bromelain-catalysed hydrolysis of N-benzyloxycarbonyl-l-phenylalanyl-l-serine methyl ester

1. Purified stem bromelain (EC 3.4.22.4) was eluted from Sephadex G-100 as a single peak. The specific activity across the elution peak was approximately constant towards p-nitrophenyl hippurate but increased with elution volume with N(2)-benzoyl-l-arginine ethyl ester as substrate. 2. The apparent molecular weight, determined by elution analysis on Sephadex G-100, is 22500+/-1500, an anomalously low value. 3. Purified stem bromelain was eluted from CM-cellulose CM-32 as a single peak and behaved as a single species during column electrophoresis on Sephadex G-100. 4. Purified stem bromelain migrates as a single band during polyacrylamide-gel electrophoresis under a wide variety of conditions. 5. The molecular weight determined by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate is 28500+/-1000. 6. Sedimentation-velocity and equilibrium-ultracentrifugation experiments, under a variety of conditions, indicate that bromelain is an apparently homogeneous single peptide chain of mol.wt. 28400+/-1400. 7. The N-terminal amino acid composition is 0.64+/-0.04mol of valine and 0.36+/-0.04mol of alanine per mol of enzyme of mol.wt. 28500. (The amino acid recovery of the cyanate N-terminal amino acid analysis was standardized by inclusion of carbamoyl-norleucine at the cyclization stage.) 8. The pH-dependence of the Michaelis parameters of the bromelain-catalysed hydrolysis of N-benzyloxycarbonyl-l-phenylalanyl-l-serine methyl ester was determined. 9. The magnitude and pH-dependence of the Michaelis parameters have been interpreted in terms of the mechanism of the enzyme. 10. The enzyme is able to bind N-benzyloxycarbonyl-l-phenylalanyl-l-serine methyl ester relatively strongly but seems unable to make use of the binding energy to promote catalysis.     

Protein kinases of rat liver endoplasmic reticulum. Solubilisation, partial characterisation and comparison with protein kinases of rat liver cytosol.

Protein kinase associated with rat liver microsomes was only partly extracted by treatment with 1.5 M KCl. The enzyme was solubilised by Triton X-100 or sodium deoxycholate at the same or slightly higher detergent concentrations than microsomal marker components. The enzyme activity increased 2-3 fold upon solubilisation. Three peaks with protein kinase activity (fractions MI, MII and MIII) were resolved on DEAE-cellulose chromatography. Fraction MIII but not fractions MI or MII was activated by adenosine 3':5'-monophosphate (cyclic AMP). All fractions catalysed the phosphorylation of protamine and histones but not that of casein or phosvitin. Fractions MI and MIII had a similar substrate specificity and phosphorylated histones at a relatively much higher rate than did fraction MII. The isoelectric points were 8.1 for fraction MI, 5.5 for fraction MII and 4.9 for fraction MIII. On incubation of fraction MIII with cyclic AMP it was split into two catalytically active components with pI 8.1 and 7.35. The component with pI 8.1 was predominant and corresponded to fraction MI. Five protein kinase peaks were resolved from rat liver cytosol by DEAE-cellulose chromatography. Three of them (fractions CIa, CIIb and CIII) had the same properties as each of the microsomal kinase fractions. A forth fraction (CIIa) was cyclic-AMP-dependent and had the same substrate specificity as fractions MI and MIII. Its pI was 5.1, and it was split into two components by cyclic AMP (pI 8.1 and 7.35). In binding studies fraction CIIb bound more efficiently to microsomes than fraction CIII, while fractions CIa, CIIa and the microsomal protein kinase fractions did not bind appreciably. When microsomes were treated with trypsin exposed protein kinase was inactivated and the latency of the remaining enzyme increased substantially. Most of fraction MII was inactivated by trypsin while fraction MIII was resistant. The possible orientation of protein kinase fractions MII and MIII in the microsomal membrane is discussed.     

Studies of the cell surface of Paramecium. Ciliary membrane proteins and immobilization antigens.

We have developed a procedure to isolate the ciliary membranes of Paramecium and have analysed the membrane proteins by electrophoresis on polyacrylamide gels containing either Triton X-100 or sodium dodecyl sulphate. The electrophoretic pattern on gels containing sodium dodecyl sulphate showed 12-15 minor bands of mol.wt. 25 000-150 000 and on major band of mol.wt. 200 000-300 000 that contained approximately three-quarters of the total membrane protein. 2. We present evidence that the major membrane protein is related to, but not identical with, the immobilization antigen (i-antigen), which is a large (250 000 mol.w.), soluble, surface protein of Paramecium. The similarity of the i-antigen and the major membrane protein was shown by immunodiffusion and by the electrophoretic mobilities in sodium dodecyl sulphate of these two proteins from Paramecium of serotypes A and B. The non-identity of these two proteins was shown by their different electrophoretic mobilities on Triton X-100 containing gels and their different solubilities. 3. We propose that the major membrane protein and the i-antigen have a precursor-product relationship.     

Secretion granules of the rabbit parotid. Selective removal of secretory contaminants from granule membranes

A membrane subfraction obtained from secretion granules isolated from rabbit parotid has been shown to be contaminated by residual secretory proteins to an estimated level of 25-30% of its total protein. In the present study an additional contaminant has been identified by improved mixing experiments and by comparative peptide mapping of specific polypeptides recovered from gels of membrane and content subfractions. This contaminant coelectrophoresis with (and probably comprises the bulk of) the majority component of the membrane subfraction (mol wt approximately 40,000). The contaminating polypeptides can be removed to a large extent by treating the membranes with low concentrations of saponin in the presence of 0.3 M Na2SO4. Although this treatment disrupts the typical bilayer structure of the granule membrane, it does not appear to cause dissociation of its phospholipids or bona fide membrane proteins.