Studies on the subunits of human myeloperoxidase.

The subunit composition of human myeloperoxidase was studied with the use of sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and gel filtration. The subunit pattern observed depended on the manner in which the enzyme was treated before analysis. Reduction before heat treatment in detergent led to two main protein species (Mr 57 000 and 10 500), whereas reduction during or after heat treatment yielded an additional species of Mr 39 000. Heating without any reductive pretreatment yielded the 39 000-Mr form as the major electrophoretic species. Carbohydrate staining showed large amounts of sugar on the 57 000-Mr species and little on the 10 500-Mr form. Significant amounts of haem were associated with this latter subunit. Haem also seemed to be associated with the 57 000-Mr form but not with the 39 000-Mr one. These three subunit forms were isolated and their amino acid composition analysed. The 57 000-Mr and 39 000-Mr forms had very similar amino acid composition and yielded an apparently identical collection of fragments on incubation with CNBr. Once separated, the subunits could not be interconverted. Generally, minor amounts of other molecular-mass forms were observed. The nature of the various molecular-mass forms originating from myeloperoxidase is discussed.     

Resolution of branched-chain oxo acid dehydrogenase complex of Pseudomonas aeruginosa PAO.

Branched-chain oxo acid dehydrogenase was purified from Pseudomonas aeruginosa strain PAO with the objective of resolving the complex into its subunits. The purified complex consisted of four proteins, of Mr 36,000, 42,000, 49,000 and 50,000. The complex was resolved by heat treatment into the 49,000 and 50,000-Mr proteins, which were separated by chromatography on DEAE-Sepharose. The 49,000-Mr protein was identified as the E2 subunit by its ability to catalyse transacylation with a variety of substrates, with dihydrolipoamide as the acceptor. P. aeruginosa, like P. putida, produces two lipoamide dehydrogenases. One, the 50,000-Mr protein, was identified as the specific E3 subunit of branched-chain oxo acid dehydrogenase and had many properties in common with the lipoamide dehydrogenase LPD-val of P. putida. The second lipoamide dehydrogenase had Mr 54,000 and corresponded to the lipoamide dehydrogenase LPD-glc of P. putida. Fragments of C-terminal CNBr peptides of LPD-val from P. putida and P. aeruginosa corresponded closely, with only two amino acid differences over 31 amino acids. A corresponding fragment at the C-terminal end of lipoamide dehydrogenase from Escherichia coli also showed extensive homology. All three peptides had a common segment of eight amino acids, with the sequence TIHAHPTL. This homology was not evident in any other flavoproteins in the Dayhoff data base which suggests that this sequence might be characteristic of lipoamide dehydrogenase.     

Evidence for preferential proteolytic cleavage of one of the two fibronectin subunits and for immunological localization of a site distinguishing them

Purified plasma fibronectin was digested sequentially by thrombin and cathepsin G or by cathepsin G alone and the degradation products and their gelatin-binding and heparin-binding fractions were analyzed in NaDodSO4-polyacrylamide gel electrophoresis followed by immunoblotting with a defined monoclonal anti-fibronectin antibody. In early cathepsin G digests, several gelatin-binding fragments were detected: a few large (Mr greater than or equal to 150 000) polypeptides and fragments of Mr = 85 000, 72 000, 64 000 and 40 000. The 85 000-Mr and 64 000-Mr fragments appeared as closely spaced doublets and reacted with the antibody while the 72 000-Mr and 40 000-Mr fragments did not. Therefore the 64 000-Mr fragments are likely to be derived from the 85 000-Mr fragments. Three large fragments that bound to heparin, but not to gelatin were detected: Mr = 145 000, 135 000 and 120 000. Of these only the 135 000-Mr peptide reacted with the antibody. When fibronectin was digested with thrombin, polypeptides of Mr = 180 000-200 000 and a 30 000-Mr NH2-terminal fragment were produced. Cathepsin G added to this mixture further cleaved the fragments to a digestion pattern resembling that obtained from intact fibronectin except that the 85 000-Mr and 64 000-Mr fragments appeared as single bands and the amount of the 72 000-Mr fragment was reduced. The results suggest that thrombin cleaves the 30 000-Mr fragment preferentially from the NH2-terminal end of one of the two subunits of fibronectin and that the 85 000-Mr, 72 000-Mr and 64 000-Mr fragments obtained by the additional cathepsin G digestion were derived from the other chain. The results are consistent with the model that the antigenic determinant resides 72 000-85 000 Da from the NH2-terminus and is cleaved by cathepsin G alternatively at one of its sides. Thus, the components of the 85 000-Mr and 64 000-Mr doublets are derived from different subunits and the region located by the antibody may be responsible for the difference in their migration in the polyacrylamide gel.     

Isolation and characterization of two major serum proteins from the dogfish, Mustelus canis, C-reactive protein and amyloid P component

Two major serum components from the dogfish, Mustelus canis, have been isolated using affinity chromatography. Both proteins bind to an AH-Sepharose 4B-phosphorylcholine affinity matrix in the presence of Ca2+ and are eluted from the column by EDTA. Upon readdition of Ca2+ to the eluted proteins, the two proteins can be separated by passage through a column of Sepharose CL-4B. The first protein, C-reactive protein, passes through the Sepharose CL-4B column in the presence of Ca2+ whereas the second protein, serum amyloid P component, remains bound. The serum amyloid P component is then eluted from the Sepharose CL-4B in pure form by EDTA. The dogfish C-reactive protein isolated by the phosphorylcholine affinity matrix precipitates with pneumococcal C-polysaccharide and with a synthetic derivative of bovine serum albumin to which phosphorylcholine is covalently attached. The precipitation is inhibited by either EDTA or by phosphorylcholine. Dogfish C-reactive protein has a molecular weight of approximately 250,000 with dimeric subunits of Mr = 50,000. Upon addition of beta-mercaptoethanol these dimeric subunits dissociate to two identical monomeric subunits of Mr = 25,000. The protein cross-reacts immunologically with goat antisera prepared against rabbit C-reactive protein. The dogfish serum amyloid P component has a molecular weight of at least 250,000 with monomeric subunits of Mr = 25,000. Cross-reactivity of the amyloid P component with the C-reactive protein could not be shown. However, NH2-terminal sequence analysis of the first 20 amino acids showed some homology. The relationship of dogfish C-reactive protein to the C-reactive proteins in Limulus polyphemus and in rabbits and humans is discussed.     

Ricin and Ricinus communis agglutinin subunits are all derived from a single-size polypeptide precursor

Antibodies have been raised in rabbits against the individually purified A and B subunits of the toxic castor bean lectin, ricin, and against the A' and B' subunits of Ricinus communis agglutinin type I. Each of the antisera recognised a single polypeptide species of Mr 60 500 when maturing castor bean endosperm mRNA was translated in vitro in a rabbit-reticulocyte-derived system. When dog pancreatic microsomal vesicles were included in the translational system, each subunit antiserum precipitated a group of 66 000-68 000-Mr core-glycosylated polypeptides which had been translocated into the lumen of the vesicles. The 60 500-Mr polypeptide appeared to be a common precursor to all four individual lectin subunits since (a) its glycosylated (66 000-68 000-Mr) forms were readily detected in the endoplasmic reticulum fraction isolated from maturing castor bean endosperm and (b) pulse-chase studies showed that the glycosylated precursors disappeared from the endoplasmic reticulum fraction with the concomittant appearance of authentic lectin subunits in a soluble protein fraction which included protein body matrix components. Antiserum prepared against whole R. communis agglutinin, type I, also precipitated the 65 000-Mr precursor in vitro and in vivo, but in addition precipitated a non-glycosylated 34 000-Mr polypeptide. This smaller protein is not a lectin subunit precursor, contradicting an earlier suggestion. It is most probably a precursor to the 2-S albumin storage proteins found in castor bean endosperm protein bodies.     

Characterization of porcine osteonectin extracted from foetal calvariae.

Osteonectin, extracted from foetal porcine calvariae with 0.5 M-EDTA, was purified to homogeneity by using gel filtration and polyanion anion-exchange fast protein liquid chromatography under dissociative conditions without the need of reducing agents. The purified protein migrated with an Mr of 40,300 on SDS/polyacrylamide gels and was similar to bovine osteonectin in both amino acid composition and in its ability to bind to hydroxyapatite in the presence of 4 M-guanidinium hydrochloride (GdmCl). However, unlike the bovine protein, porcine osteonectin did not bind selectively to hydroxyapatite when EDTA tissue extracts were used. In addition, purified porcine osteonectin did not show any apparent affinity for either native or denatured type I collagen, but did bind to serum albumin. Primary sequence analysis revealed an N-terminal alanine residue, with approximately one-half of the subsequent 35 residues identified as small hydrophobic amino acids and one-quarter as acidic amino acids. The only significant difference between the N-terminal sequences of the bovine and porcine proteins was the deletion of the tripeptide Val-Ala-Glu in porcine osteonectin. In contrast with bovine osteonectin, far-u.v.c.d. of porcine osteonectin revealed considerable secondary structure, of which 27% was alpha-helix and 39% was beta-sheet. Cleavage of the molecule with CNBr under non-reducing conditions generated five fragments, of which two major fragments (Mr 27,900 and 12,400) stained blue with Stains All, a reagent that stains sialic-acid-rich proteins/phosphate-containing proteins and/or Ca2+-binding proteins blue while staining other proteins pink. The 12,400-Mr fragment bound 45Ca2+ selectively, indicating a Ca2+-binding site in this part of the molecule. The 27,900-Mr fragment did not bind Ca2+, and since biosynthetic studies with 32PO4(3-) did not show phosphorylation of porcine osteonectin, this fragment is likely to be highly acidic. The incomplete cleavage of the molecule with CNBr and the ability of the molecule to regain its secondary structure after exposure to 7 M-urea are features consistent with the molecule having a compact structure that is stabilized by numerous disulphide bridges. The chemical and binding properties of porcine osteonectin are closely similar to the recently described 'culture shock', SPARC and BM-40 proteins, indicating that these are homologous proteins.     

Structural characteristics and intermolecular organization of human pulmonary-surfactant-associated proteins.

The structural relationships and intermolecular organization among the proteins associated with pulmonary surfactant are largely unknown. We studied the pulmonary-surfactant-associated proteins in the bronchoalveolar lavage fluid obtained from a patient with the clinical syndrome of alveolar proteinosis. The major proteins with Mr values of 32,000-36,000 and 62,000 formed thiol-dependent complexes (Mr greater than 400,000) with intermolecular disulphide bonds present in the collgenase-sensitive domains of these proteins. In contrast, other proteins, which were collagenase-insensitive, formed thiol-dependent oligomers that were not covalently linked to the major proteins. The associations of these proteins in the surfactant of a normal individual were similar. By amino acid analysis, two-dimensional peptide mapping and bacterial-collagenase digestion the 32,000-36,000-Mr and 62,000-Mr proteins were nearly identical. Differences in CNBr cleavage products suggested that the larger of the proteins was formed by non-disulphide, covalent, cross-links in the collagenase-sensitive domains of the 32,000-36,000-Mr proteins. Thus the evidence suggested that the lipid-associated proteins of Mr 32,000-36, 000 contained both disulphide and non-disulphide cross-links in the collagen-like N-terminal region of the proteins and form higher-Mr complexes. This organization may support the three-dimensional conformation of surfactant in the alveolar space.     

Heart contains two substrates (Mr = 40,000 and 41,000) for pertussis toxin-catalyzed ADP-ribosylation that co-purify with Ns

Two peptides (Mr = 40,000 and 41,000) in membranes of rabbit heart are radiolabeled when the membranes are incubated in the presence of activated pertussis toxin and [32P]NAD+. The 41,000-Mr peptide appears to be the alpha subunit of the inhibitory regulatory protein of adenylate cyclase, Ni. The 40,000-Mr substrate for pertussis toxin in the heart was investigated. Purification of the stimulatory regulatory protein of adenylate cyclase, Ns, results in the co-purification of the alpha subunits of both Ns and Ni, the putative beta- (Mr = 35,000) and gamma- (Mr approximately equal to 15,000) subunits of Ns and Ni, and the additional 40,000-Mr peptide that is ADP-ribosylated by pertussis toxin. This 40,000-Mr substrate for pertussis toxin action appears to be a major N-protein of mammalian heart.     

The calmodulin-dependent glycogen synthase kinase from rabbit skeletal muscle. Purification, subunit structure and substrate specificity

A calmodulin-dependent glycogen synthase kinase distinct from phosphorylase kinase has been purified approximately equal to 5000-fold from rabbit skeletal muscle by a procedure involving fractionation with ammonium sulphate (0-33%), and chromatographies on phosphocellulose, calmodulin-Sepharose and DEAE-Sepharose. 0.75 mg of protein was obtained from 5000 g of muscle within 4 days, corresponding to a yield of approximately equal to 3%. The Km for glycogen synthase was 3.0 microM and the V 1.6-2.0 mumol min-1 mg-1. The purified enzyme showed a major protein staining band (Mr 58 000) and a minor component (Mr 54 000) when examined by dodecyl sulphate polyacrylamide gel electrophoresis. The molecular weight of the native enzyme was determined to be 696 000 by sedimentation equilibrium centrifugation, indicating a dodecameric structure. Electron microscopy suggested that the 12 subunits were arranged as two hexameric rings stacked one upon the other. Following incubation with Mg-ATP and Ca2+-calmodulin, the purified protein kinase underwent an 'autophosphorylation reaction'. The reaction reached a plateau when approximately equal to 5 mol of phosphate had been incorporated per 58 000-Mr subunit. Both the 58 000-Mr and 54 000-Mr species were phosphorylated to a similar extent. Autophosphorylation did not affect the catalytic activity. The calmodulin-dependent protein kinase initially phosphorylated glycogen synthase at site-2, followed by a slower phosphorylation of site-1 b. The protein kinase also phosphorylated smooth muscle myosin light chains, histone H1, acetyl-CoA carboxylase and ATP-citrate lyase. These findings suggest that the calmodulin-dependent glycogen synthase kinase may be a enzyme of broad specificity in vivo. Glycogen synthase kinase-4 is an enzyme that resembles the calmodulin-dependent glycogen synthase kinase in phosphorylating glycogen synthase (at site-2), but not glycogen phosphorylase. Glycogen synthase kinase-4 was unable to phosphorylate any of the other proteins phosphorylated by the calmodulin-dependent glycogen synthase kinase, nor could it phosphorylate site 1 b of glycogen synthase. The results demonstrate that glycogen synthase kinase-4 is not a proteolytic fragment of the calmodulin-dependent glycogen synthase kinase, that has lost its ability to be regulated by Ca2+-calmodulin.     

Storage protein precursor polypeptides in cotyledons of Pisum sativum L. Identification of, and isolation of a cDNA clone for, an 80000-Mr legumin-related polypeptide

An 80 000-Mr polypeptide, which bound to anti-legumin IgG, was detected among labelled polypeptides from cotyledons at late stages of development. When poly(A)-containing RNA from similar cotyledons was translated in a cell-free protein-synthesizing system, an 80 000-Mr polypeptide was also detected. Immunoprecipitation of translation products with anti-legumin IgG showed that, in addition to the major legumin precursor polypeptides of Mr approximately 60 000, the 80 000-Mr polypeptide was specifically immunoprecipitated. A cDNA clone, pCD32, was found to select an RNA coding for an 80 000-Mr polypeptide in hybrid-selection experiments. Additional minor polypeptides of Mr 63 000 and 65 000 were present in translation products of RNA selected by pCD32; all three polypeptides were immunoprecipitated by anti-legumin IgG. Thermal elution of RNAs bound to pCD32 showed that the affinity of pCD32 to the RNA coding for the 80 000-Mr polypeptide was greater than to the RNAs coding for the 63 000-Mr and 65 000-Mr polypeptides. In similar hybrid-selection experiments, another cDNA clone, pCD40, selected RNAs coding predominantly for polypeptides of Mr 63 000 and 65 000. A minor polypeptide of Mr 80 000 was also detected among these products; again all three polypeptides were immunoprecipitated by anti-legumin IgG. Peptide mapping revealed close similarities between the 80000-Mr polypeptide and the 63 000-Mr/65 000-Mr polypeptides obtained by translation of RNAs selected by pCD32. There were similarities also between maps obtained from translation products of RNA selected by pCD32 and those obtained from anti-legumin IgG immunoprecipitates of total translation products of poly(A)-containing RNA.     

Affinity purification and subunit structures of beta-N-acetylhexosaminidases A and B from boar epididymis.

beta-N-Acetylhexosaminidase from boar epididymis was separated into two forms, A and B, on DEAE-cellulose. Both these forms were excluded from Sepharose S-200 and had apparent Mr values of 510 000 on gradient gel electrophoresis under non-denaturing conditions. Affinity chromatography on 2-acetamido-N-(6-aminohexanoyl)-2-deoxy-beta-D-glucopyranosylam ine coupled to CNBr-activated Sepharose 4B was used to separate and purify beta-N-acetylhexosaminidases A and B that had specific activities of 115 and 380 mumol/min per mg of protein respectively. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of denatured beta-N-acetylhexosaminidase A gave a single major component of Mr 67 000. beta-N-Acetylhexosaminidase B also had this component, and in addition had polypeptides of Mr 29 000 and 26 000. All these polypeptides were glycosylated. Antiserum to the B form precipitated form A from solution and reacted with the 67 000-Mr component or form A after electrophoretic transfer from sodium dodecyl sulphate/polyacrylamide gels to nitrocellulose sheets. The 67 000-Mr components of forms A and B yielded identical peptide maps when digested with Staphylococcus aureus V8 proteinase, and the 29 000-Mr and 26 000-Mr components in form B may be related to the 67 000-Mr polypeptide.     

Mitochondrial polypeptide elongation factor EF-Tu of Saccharomyces cerevisiae. Functional and structural homologies to Escherichia coli EF-Tu

The polypeptide elongation factor EF-Tu was isolated from a mitochondrial 100 000 x g supernatant of the yeast Saccharomyces cerevisiae and purified over 880-fold by DEAE-Sephadex chromatography and gel filtration. The factor efficiently replaces bacterial EF-Tu in a phenylalanine polymerizing cell-free system of Escherichia coli, it binds GDP and it protects phenylalanyl-tRNA against hydrolysis of the ester bond in the presence of 10 mM GTP. The polymerizing activity of the mitochondrial factor is inhibited to 90% by 50 microM N-ethylmaleimide and to 50% by 2.5 microM kirromycin. The purified factor contains two major polypeptides of apparent molecular weights 48 000 and 34 000. Antibodies raised against the 48 000-Mr protein react with EF-TuE. coli, as revealed by immune blotting and by the inhibition of phenylalanine polymerization. No reaction was observed between anti-(34 000-Mr) and 48 000-Mr protein or EF-TuE. coli. The 48 000-Mr protein has the same isoelectric point (pI = 6.2) and a content of cysteine and basic amino acids similar to the bacterial EF-Tu. It is concluded that the 48 000-Mr protein is the analogue to EF-TuE. coli, and that yeast mitochondrial EF-Tu is functionally and structurally more related to bacterial EF-Tu than cytosolic EF-1 of the same cell.     

Ca2+-binding proteins from bovine brain including a potent inhibitor of protein kinase C.

We have previously described the use of Ca2+-dependent hydrophobic-interaction chromatography to isolate the Ca2+ + phospholipid-dependent protein kinase (protein kinase C) and a novel heat-stable 21 000-Mr Ca2+-binding protein from bovine brain [Walsh, Valentine, Ngai, Carruthers & Hollenberg (1984) Biochem. J. 224, 117-127]. The procedure described for purification of the 21 000-Mr calciprotein to electrophoretic homogeneity has been modified to permit the large-scale isolation of this Ca2+-binding protein, enabling further structural and functional characterization. The 21 000-Mr calciprotein was shown by equilibrium dialysis to bind approx. 1 mol of Ca2+/mol, with apparent Kd approx. 1 microM. The modified large-scale purification procedure revealed three additional, previously unidentified, Ca2+-binding proteins of Mr 17 000, 18 400 and 26 000. The 17 000-Mr and 18 400-Mr Ca2+-binding proteins are heat-stable, whereas the 26 000-Mr Ca2+-binding protein is heat-labile. Use of the transblot/45CaCl2 overlay technique [Maruyama, Mikawa & Ebashi (1984) J. Biochem. (Tokyo) 95, 511-519] suggests that the 18 400-Mr and 21 000-Mr Ca2+-binding proteins are high-affinity Ca2+-binding proteins, whereas the 17 000-Mr Ca2+-binding protein has a relatively low affinity for Ca2+. Consistent with this observation, the 18 400-Mr and 21 000-Mr Ca2+-binding proteins exhibit a Ca2+-dependent mobility shift on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, whereas the 17 000-Mr Ca2+-binding protein does not. The amino acid compositions of the 17 000-Mr, 18 400-Mr and 21 000-Mr Ca2+-binding proteins show some similarities to each other and to calmodulin and other members of the calmodulin superfamily; however, they are clearly distinct and novel calciproteins. In functional terms, none of the 17 000-Mr, 18 400-Mr or 21 000-Mr Ca2+-binding proteins activates either cyclic nucleotide phosphodiesterase or myosin light-chain kinase, both calmodulin-activated enzymes. However, the 17 000-Mr Ca2+-binding protein is a potent inhibitor of protein kinase C. It may therefore serve to regulate the activity of this important enzyme at elevated cytosolic Ca2+ concentrations.     

Disparate effects of monensin and colchicine on intracellular processing of secretory proteins in cultured rat hepatocytes

We have studied the biosynthesis and intracellular processing of three major secretory proteins, albumin, alpha 1-protease inhibitor and alpha 2u-globulin, in cultured rat hepatocytes. The effect of secretion-blocking agents, monensin, a monovalent ionophore, and the microtubule-affecting agents colchicine and taxol was determined. In the control cells, alpha 1-protease inhibitor, a glycoprotein, was first synthesized as an endoglycosidase-H-sensitive form with Mr 51 000, and then processed to two endoglycosidase-H-resistant forms having Mr 51 000 and 56 000, the latter of which was secreted into the medium. Initially synthesized proalbumin was converted with chase to serum-type albumin, while no pro-type precursor was identified for alpha 2u-globulin. In the cells treated with colchicine or taxol, in which secretion was greatly inhibited, the fully processed alpha 1-protease inhibitor and albumin accumulated and were finally secreted into the medium. In the monensin-treated cells, however, most of the newly synthesized alpha 1-protease inhibitor and albumin were not processed to the final mature forms, resulting in accumulation of two 51 000-Mr forms and proalbumin, respectively. Moreover in treated cells, proalbumin and the endoglycosidase-H-resistant alpha 1-protease inhibitor were finally secreted into the medium. Such an effect was not caused by NH4Cl which also inhibited the secretion and is known to exert the similar effect as monensin on the receptor-mediated endocytosis pathway. Based on these results, the use of monensin may prove valuable for more detailed analysis of intracellular processing of various proteins.     

Mouse alpha-macroglobulin. Structure, function and a molecular model.

Mouse alpha-macroglobulin (M-AMG) is believed to be a functional homologue of human alpha 2-macroglobulin (h-alpha 2M). The subunit composition, the tryptic cleavage pattern before and after methylamine incorporation and the two-dimensional tryptic-peptide mapping, however, indicate that these two proteins are structurally distinct. M-AMG is composed of two major types of polypeptides (Mr 163,000 and 35,000) together with a minor polypeptide (Mr 185,000), whereas h-alpha 2M has only one type of polypeptide (Mr 185,000). After incorporation of methylamine, there is no change in the normal tryptic-cleavage pattern of M-AMG; however, tryptic cleavage of h-alpha 2M is severely retarded [Hudson & Koo (1982) Biochim. Biophys. Acta 704, 290-303]. The N-terminal sequence of the 163,000-Mr polypeptide of M-AMG shows sequence homology with the N-terminal sequence of h-alpha 2M. The amino acid compositions of M-AMG and its two major polypeptide chains are compared. Thermal fragmentation studies show that the 163,000-Mr polypeptide is broken down into 125,000-Mr and 29,000-Mr fragments. Trypsin-binding studies show that M-AMG can bind two molecules of trypsin/molecule. Inactivations of the trypsin-binding property of M-AMG and h-alpha 2M with methylamine show similar kinetics of inhibition at 4 degrees C. A structural model of M-AMG is proposed, based on accumulated data.     

Apolipoprotein A-IV: a protein occurring in human mesenteric lymph chylomicrons and free in plasma. Isolation and quantification.

1. Human mesenteric lymph chylomicrons were isolated from chylous ascites fluid by ultra-centrifugation and agarose/gel chromatography and their apoprotein composition was analysed by dodecylsulfate/polyacrylamide gel electrophoresis, analytical isoelectric focusing and immuno-chemically. Major components of mesenteric lymph chylomicrons were apoprotein A-I, proteins of Mr less than 15 000 including the C-group apoproteins and a protein of Mr 46 000. Minor components were apoprotein E and a protein of Mr approximately equal to 200 000 (B-like protein). This apoprotein composition was qualitatively identical with that of chylomicrons from intestinal lymph of the rat, but was distinctly different from plasma chylomicrons of humans with fasting chylomicronaemia. 2. The protein of Mr approximately equal to 46 000 has been isolated by preparative dodecylsulfate/polyacrylamide gel electrophoresis from human and rat lymph chylomicrons and was compared to a protein of identical Mr present in rat high-density lipoproteins (apoplipoprotein A-IV) and in the rho less than 1.006 g/ml serum lipoprotein fraction of individual humans with alimentary hypertriglyceridaemia. In both species the 46 000-Mr proteins isolated from lymph and serum were identical according to amino acid composition and isoelectric point in 6 M urea. The human proteins from both sources were also immunologically identical. The similarities in the molecular properties of the human apolipoprotein and rat apolipoprotein A-IV indicate that these proteins are homologous. 3. Plasma levels of human apolipoprotein A-IV determined by electroimmunodiffusion were 14.15 +/- 3.66 mg/100 ml (n = 59), but greater than 90% of the protein was unassociated with the major lipoprotein fractions. It is concluded, that apolipoprotein A-IV is a main protein component of human lymph chylomicrons, that is removed from the particles in the plasma compartment.     

Changes in salt-soluble proteins of rice during grain development

Salt-soluble proteins, albumin and globulin, were prepared from dehulled rice (Oryza sativa L., line IR1541-76-3) during grain development. Albumin and globulin progressively increased during grain development up to about 12 days after flowering (DAF) and then decreased slightly during grain desiccation. Free amino N was maximum at 10 DAF. Total protein and glutelin-prolamin (by difference) continued to increase up to 20 DAF. Aminogram of total protein and globulin showed a progressive decrease in lysine and threonine among the essential amino acids. Albumin showed a similar trend except for the lesser change in lysine content. Disc gel electrophoresis showed a maximum of four major and six minor protein bands for albumin and only one major and three minor bands for globulin. Sodium dodecyl sulfate-gel electrophoresis revealed three major polypeptide subunits for albumin with MW of 11 000, 8 500 and 16 000, and two for globulin with MW of 20 000 and 12 000.     

Characterization of the protein moiety of messenger ribonucleoprotein complexes from duck reticulocytes by two-dimensional polyacrylamide gel electrophoresis.

The protein moiety of duck globin messenger ribonucleoprotein complexes isolated by oligo(dT)-cellulose chromatography or by sucrose gradient centrifugation was analysed by two-dimensional polyacrylamide gel electrophoresis under conditions where the separation in the first dimension occurs according to charge and in the second according to molecular weight. By comparing the pattern of protein from the mRNA - protein complex with that of ribosomal subunits we found that two acidic proteins with an identical molecular weight of about 49 000 and three basic proteins of about Mr 56 000, 64 000 and 73 000 were associated with the duck globin mRNA but were absent from either puromycin/high-salt-derived or 'run-off' ribosomal subunits. The comparison of the proteins from the complex with mRNA with those found in the 0.5 M KCl wash, commonly used as the source of initiation factors, showed also that only the 49 000-Mr protein from the complex could possibly be present in the 0.5 M KCl wash of polyribosomes; proteins with mobilities similar to the other three proteins complexed with mRNA were not detected in the salt wash of polyribosomes.     

Purification and characterization of a plasminogen activator secreted by a pig kidney cell line

The plasminogen activator secreted by calcitonin-treated pig kidney cells was purified, characterized and compared with human urinary urokinase. The purification procedure was based on the following steps: sulphopropyl-Sephadex chromatography, p-aminobenzamidine-Sepharose chromatography, preparative sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectrofocusing. The purified enzyme was obtained from the conditioned medium with a yield of 13% and a purification factor of 390-fold. Analysis by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under non-reducing conditions showed one closely spaced doublet with an Mr of 50 000; in the presence of reducing agents, two additional bands of Mr 30 000 and 20 000 appeared. The purified enzyme resembles the 53 000-Mr components of human urinary urokinase in amino acid composition and two-dimensional tryptic peptide maps and in its catalytic properties, and the two enzymes cross-react immunologically with rabbit antibodies raised against either. The enzyme appears to be different from tissue plasminogen activator secreted by HeLa cells.