Immunoglobulin biosynthesis. IV. Carbohydrate attachment to immunoglobulin subunits

Protein G binding to enriched serum immunoglobulin from nondomestic hoofstock species

Quick and cost-effective serologic assays, such as those based on enzyme-linked immunosorbent assay (ELISA) technology, are useful for screening animal populations for infectious diseases. Recombinant protein G is described as an almost universal ELISA conjugate for the detection of antibodies from a wide range of animal species. However, there is limited data documenting the ability of protein G to bind immunoglobulin (Ig) from many captive and free-ranging nondomestic hoofstock (Order Artiodactyla, e.g., elk, antelope, bison). Protein G binding to Ig from 11 species within this taxonomic order (addax, antelope, bison, bontebok, elk, impala, kudu/nyala, muntjac, oryx, sheep, and white-tailed deer) and 2 control species (bovine and chicken) was assessed. A serum Ig enrichment protocol, using high-performance liquid chromatography (HPLC), was optimized in bovids (Bos taurus) and then applied to the other study species. Binding assays were performed by adding protein G to microtiter wells coated with titrated dilutions of enriched artiodactyl Ig. Optical densities were measured and binding curves generated. Differences in protein G binding were observed, both within and among species, as well as within taxonomic families. Significant intraspecies binding variation was observed for 7 species tested (antelope, oryx, sheep, muntjac, impala, bontebok, and addax). No statistically significant intraspecies differences in protein G binding were found for Ig from bison, elk, kudu/nyala, white-tailed deer, plus control species (cattle and chicken). Binding of protein G to Ig from impala, muntjac, and elk was statistically different from the positive control (cattle), with muntjac binding curves statistically comparable with the negative control (chicken). For the other 7 species tested, binding curves illustrated the ability of protein G to bind Ig as well as, or better than, the positive control. These findings expand the list of animal species whose Ig is capable of being detected using recombinant protein G, with the caveat that protein G does not bind Ig uniformly in closely related species. It is concluded that recombinant protein G conjugates may serve as useful reagents for serodiagnosis by ELISA in nondomestic hoofstock, although different assay interpretation algorithms and assay protocols may need to be developed on a per species basis for maximum diagnostic effectiveness.

Characterization and cloning of two isoforms of heteroglobin, a novel heterodimeric glycoprotein of the secretoglobin-uteroglobin family showing tissue-specific and sex differential expression

Heteroglobin (HGB) is a 39-kDa heterodimeric protein detected under non-reducing conditions in harderian, parotid, and submaxillary glands and saliva of the Syrian hamster with antiserum raised against the carboxyl end deduced from the female harderian gland cDNA FHG22 (Dominguez, P. (1995) FEBS Lett. 376, 257-261). After reduction, only one 5.6-kDa polypeptide, named HGB.A, was immunodetected and identified by sequencing as the mature FHG22 product. Tissue-specific expression of HGB.A and HGB mimics that of FHG22 mRNA, with sex differences in submaxillary and harderian glands. Purification of HGB revealed it consists of HGB.A disulfide bonded to HGB.B, a 33.5-kDa N-glycosylated subunit that yields a 9-kDa core polypeptide after deglycosylation. Two highly homologous (96.2%) cDNA clones (HGB.B1 and HGB.B2) encoding 94 amino acid-long isoforms were identified by screening a female harderian gland library with an HGB.B probe. The corresponding mature polypeptides are 78 amino acids long with 12 differences, but 3 putative N-glycosylation sites are maintained. The expression of HGB.B mRNAs is parallel to that of HGB and HGB.A, but no HGB.B2 mRNA was detected in submaxillary glands. Homology studies indicate that HGB.A and HGB.B1/HGB.B2 belong to different subfamilies of the secretoglobin-uteroglobin family and form heterodimers as previously described.

Microbial amylolytic enzymes

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Heterogeneous glycosylation of murine transferrin receptor subunits

The N-linked glycosylation of the murine receptor for transferrin has been investigated. Previously we have found that purified receptors appear as two bands after sodium dodecyl sulfate/polyacrylamide gel electrophoresis and Coomassie blue staining [van Driel, I.R., Stearne, P.A., Grego, B., Simpson, R.J. and Goding, J.W. (1984) J. Immunol. 133, 3220-3224]. In the current report we show that the two bands are due to different glycosylation of individual receptor molecules. The receptors have three asparagines to which N-linked glycans can be added, but only two sites are glycosylated in all receptors. The level of glycosylation of the third site varies depending on cell line or tissue. Limited endoglycosidase digestion of mature receptors indicates that differential glycosylation probably occurs at only one particular asparagine residue. Possible mechanisms that could result in such a glycosylation pattern are discussed.

On the various forms of the glandular kallikrein from autolyzed porcine pancreas

Kallikrein C, a minor form of the glandular kallikrein isolated form autolyzed porcine pancreas, has the same amino acid composition a porcine pancreatic beta-kallikreins A and B and comparable specific activity, but a much lower carbohydrate content. Dodecyl sulfate electrophoresis of the reduced enzyme indicated that it is composed of the same two polypeptide chains as the other pancreatic beta-kallikreins of the pig. The carbohydrate content of the two chains of beta-kallikrein B has been determined. Both the A and the B chain of beta-kallikreins from autolyzed porcine pancreas exist in a high-molecular (h) and a low-molecular (1) form which evidently differ only in their carbohydrate content. beta-Kallikrein B has the composition AhBh, beta-kallikrein A, AhB1, and beta-kallikrein C, A1B1. The properties of kallikrein III from porcine pancreas, recently described by Kira et al. (Adv. Exp. Med. Biol. 120A (1979) 273--290), indicate that is is the fourth conceivable form, A1Bh. A preparation of porcine pancreatic kallikrein d2 was found to have a specific activity comparable to that of other kallikrein preparations. Besides a main component migrating like pancreatic beta-kallikrein A, it also contained beta-kallikreins B and C. All four species of chains were observed to occur in this batch of the enzyme. Zuber and Sache (Biochemistry 13 (1974) 3098--3110) reported the resolution of porcine pancreatic kallikreins d1 and d2 into three electrophoretic components each after reduction. Evidently, all these preparations consist of a mixture of several forms of two-chain pancreatic beta-kallikrein.

Characterization of a self-associating glycoprotein from bovine ligamentum nuchae exhibiting dual amine oxidase activity

A homogeneous preparation of glycoprotein (apparent molecular weight 34,000) has been isolated from bovine ligamentum nuchae by treatment of the tissue with 5 M guanidine HCl and 2-mercaptoethanol. The preparation exhibits amine oxidase activity which is only marginally inhibited by beta-aminopropionitrile.

Characterization of surface proteins and glycoproteins on red blood cells from mice infected with haemosporidia: Plasmodium yoelii infections of BALB/c mice

Lactoperoxidase-catalysed radio-iodination was used to compare the surface proteins on red cells from Plasmodium yoelii-infected with normal BALB/c mice. The profile of radio-iodinated proteins separated by SDS-polyacrylamide gel electrophoresis was different for infected blood of similar parasitaemia from mice inoculated with different doses of the parasite. Inoculation with different doses of the parasite. Inoculation with the lower dose resulted in the appearance of a major radio-iodinated protein of apparent molecular weight (Mr) 76 000 which was labelled to a similar extent on uninfected red cells from infected blood and purified multinucleate infected cells. Several minor radio-iodinated bands, with identical mobilities to the minor bands on normal BALB/c erythrocytes, were also present on red cells from this infected blood. In contrast, the higher inoculation dose produced changes in the minor labelled bands, and the band with Mr of 76 000 was absent. In this case, the minor radio-iodinated proteins of the normal BALB/c erythrocyte (with Mr of 65 000, 57 000, 48 000, 38 000 and 32 000) were replaced by a series of bands with Mr of 60 000, 50 000, 43 000 and 28 000 on both uninfected and infected red cells. These differences with inoculation dose may be related to the different duration of these infections, the development of anaemia and the extent of pathological changes at the erythrocyte surface. P. yoelii infection caused a marked loss in periodate-dependent labelling of sialoglycoproteins on most, if not all, red cells in infected blood. There was also a large decrease in galactose oxidase-dependent glycoprotein labelling with or without neuraminidase treatment. These changes in the carbohydrate groups on red cell membrane glycoproteins may be linked to the excessive loss of both uninfected and infected red cells during some malaria infections.

Characterization of surface proteins and glycoproteins on red blood cells from mice infected with haemosporidia: Plasmodium berghei infections of BALB/c mice

The surface proteins and glycoproteins of red cells from Plasmodium berghei-infected blood have been radio-isotope labelled and compared with those of normal mouse erythrocytes using the following protein labelling probes: lactoperoxidase-catalysed radio-iodination of tyrosyl residues, periodate oxidation and NaB3H4 reduction of sialic acid and oxidation of galactosyl/N-acetylgalactosaminyl residues by galactose oxidase with subsequent NaB3H4 reduction. During P. berghei infection, new tyrosyl-labelled proteins with apparent molecular weights (Mr) of 60 000, 54 000, 40 000 and 27 500 appeared on the surface of most, if not all, red cells in the blood. Purified multinucleate cells (mostly reticulocytes) differed only in that they also had a surface protein with Mr of 83 000. However, this molecule is thought to be specific to mouse reticulocytes rather than derived from parasites. In contrast to the relatively minor changes detected with radio-iodination, striking changes in glycoprotein radio-isotope labelling resulted from infection. All of the red cells in infected blood of greater than 20% parasitaemia lost their periodate-sensitive glycoprotein sialic acid. With some samples there was little change in glycoprotein labelling by the galactose oxidase method, provided neuraminidase was also added. Modification of the exocyclic hydroxyls of sialic acid is postulated to account for this. Other blood samples exhibited a dramatic loss of galactose oxidase-dependent labelling. It is suggested that these observations may relate to the excessive red cell destruction of uninfected as well as infminidase was also added. Modification of the exocyclic hydroxyls of sialic acid is postulated to account for this. Other blood samples exhibited a dramatic loss of galactose oxidase-dependent labelling. It is suggested that these observations may relate to the excessive red cell destruction of uninfected as well as infminidase was also added. Modification of the exocyclic hydroxyls of sialic acid is postulated to account for this. Other blood samples exhibited a dramatic loss of galactose oxidase-dependent labelling. It is suggested that these observations may relate to the excessive red cell destruction of uninfected as well as infected cells which has been inferred in many haemosporidial infections, including malaria.

A calcium binding IgG myeloma protein

A calcium binding IgG was isolated and purified by column chromatography from serum of a myeloma patient with asymptomatic hypercalcaemia. The myeloma IgG, characterized as an IgG kappa, revealed a normal sized heavy chain (56 000 dalton), and a light chain of 31 000 dalton. Another population of IgG separated and purified from the same patient's serum did not bind calcium and had a normal 26 000 dalton light chain. Calcium binding activity in vitro is optimal at pH 8.0, and reaches its maximum after 3 h of 45Ca myeloma IgG incubation. Cleavage of the purified IgG by trypsin yielded peptides which were further isolated by column chromatography and characterized as Fab and Fc fragments. Light and heavy chains were obtained by reacting the immunoglobulin with dithiothreitol and iodoacetamide followed by Sephadex G-100 chromatography. Calcium binding activity was proved to be associated with Fab IgG fragment. Preparates containing Fc, heavy or light chains did not bind calcium in vitro.

Purification, characterization and identification of an agglutinin in human serum

A serum protein named agglutinin is able to induce mitochondria to agglutinate. The protein has been purified from human serum by chromatography on DE-52. Sephadex G-200 and immunoglobulin-Sepharose 4B columns. Agglutinin is a glycoprotein that migrates electrophoretically as a gamma-globulin. Its molecular weight was determined to be 50,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Monospecific antiserum prepared against the agglutinin was found to be identical with anti-beta 2-glycoprotein I and agglutinating activity could be adsorbed on anti-beta 2-glycoprotein I-Sepharose 4B columns. Thus, the agglutinin has been identified as beta 2-glycoprotein I. The reaction between mitochondria and agglutinin shows positive cooperativity, which is independent on the stage of purification of agglutinin. The agglutinating activity could be diminished (inhibited) by acidic non-soluble lipids such as oleic acid, phosphatidic acid, phosphatidyl serine and phosphatidyl inositol.

Nonsecreting myeloma variants with heavy-chain carbohydrate deficiencies

Light- and heavy-chain synthesis was studied in six previously isolated S194-2 mouse myeloma variant lines and in the parent from which they were derived. Serological data and comparative analysis of the cyanogen bromide fragments obtained from variant and parent intracellular immunoglobulin showed that five variants which failed to secrete detectable amounts of IgA synthesized both heavy- and light-chain subunits. Whereas at least two heavy-chain populations were resolved in the parent line, one containing carbohydrate and one devoid of carbohydrate, only the heavy-chain fraction devoid of carbohydrate was detected in the variant lines. The correlation between carbohydrate deficiencies on the heavy chains and lack of immunoglobulin secretion in five independent subclones is discussed in terms of possible primary lesions and the role of carbohydrate in secretion.

Sheep prothrombin: purification and partial characterization

A procedure for the preparation of highly purified sheep prothrombin is described. The purified zymogen, when subjected to disc gel electrophoresis in polyacrylamide, gave rise to one single band. Only alanine was found as N-terminal residue. Carboxypeptidases A and B failed to release any C-terminal residue. The isoelectric point, as determined by isoelectric focusing in polyacrylamide gel slab, was shown to be 4.9-5.0. Non-chromatographed, but not the purified zymogen, could be converted into active thrombin in half-saturated trisodium citrate seeded with thrombin. Pure sheep prothrombin showed 5.6% of neutral sugars and the following amino acid composition: Ala35, Arg44, Asx54-55, -Cys24, Glx72, Gly53-54, His8, Ile19, Leu45, Lys31, Met7, Phe23, Pro36, Ser34, Thr29-29, Trp16, Tyr19 and Val33, which accounts for a molecular weight of about 66 000 (amino acids only). The molecular weight as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis after reduction by 2-mercaptoethanol, was shown to be 77 000 +/- 3000 (carbohydrates included).

Human liver alkaline phosphatase purified by affinity chromatography, ultracentrifugation and polyacrylamide-gel electrophoresis

A method is presented for the preparation of human liver alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1). The method gives a purification factor of 12.5 X 10(3) over the initial aq. butan-1-ol extract, a recovery of 6.0% and a specific activity for the preparation of 1450-1550 units/mg of protein, 1 unit being defined as the amount of enzyme catalysing the hydrolysis of 1mumol of p-nitrophenyl phosphate/min at 35 degrees C in 0.1 M-2-amino-2-methylpropan-1-ol/HCl buffer, pH 10.5, containing 10mM-p-nitrophenyl phosphate. Homogeneity was studied by ultracentrifugation, by immunoelectrophoresis and by polyacrylamide-gel electrophoresis. A single contaminating protein was present which was less than 5% of the total. Ultracentrifugation and equilibrium-gradient-pore electrophoresis techniques indicated a mol.wt. of 156000 and 160000 respectively. Equilibrium-gradient-pore electrophoresis indicated that the alkaline phosphatase molecule is possibly a dimer, comprising two subunits of about 80000 mol.wt. Amino acid analysis proved remarkably similar to that for alkaline phosphatase from other sources, regardless of species.

Esterification of J chain and its effect on electrophoretic mobility in sodium dodecyl sulfate polyacrylamide gels

Sodium dodecyl sulfate polyacrylamide gel electrophoresis yields mobilities indicative of molecular weights of approximately 27 000 for human J chain and approximately 14 000 for nurse shark J chain, in contrast to values of approximately 15 500 and approximately 12 200, respectively, obtained by other methods. The relatively high content of acidic amino acids of human J chain as compared to nurse shark J chain suggested that the greater error in the sodium dodecyl sulfate determined molecular weight for human J chain may be due to a charge anomaly. The overall net negative charge on human J chain was decreased by forming methyl esters of the carboxyl groups, resulting in a sodium dodecyl sulfate determined molecular weight of approximately 17 700. Methylated nurse shark J chain did not show a significant difference in sodium dodecyl sulfate electrophoretic mobility from the non-methylated form. These results form the basis for a possible explanation of an occasional artifact in a widely used analytical method.

Three structural polypeptides coded for by minite virus of mice, a parvovirus

Purified full and empty virions of minute virus of mice were separated on CsCl gradients, and their polypeptides were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The empty particle contains two polypeptides, A (83,300 daltons) and B (64,300 daltons), which are 15 to 18% and 82 to 85%, respectively, of the virion mass. The full particle contains the single-stranded DNA genome, proteins A and B, and a third polypeptide, C (61,400 daltons). Again A is 15 to 18% of the protein mass, but the amounts of B and C vary inversely in different preparations of full particles. These polypeptides comprise greater than 99.6% of the protein in either virion, and their molecular weights and molar ratios are independent of the species of host cell on which the virus is propagated, They are not found in uninfected cells, and no protein component of uninfected cells copurifies with either virion under our conditions. Pulse-chase experiments show that the three proteins are synthesized only after virus infection and are therefore probably virus coded. Sequential harvesting from the nuclei of cells infected under one cycle growth conditions shows an increase in the proportion of C in full particles as infection progresses, suggesting that C is derived from B in a late maturation step.

The cytochrome bc1 complex of yeast mitochondria. Isolation and partial characterization of the cytochrome bc1 complex and cytochrome b

We have isolated the cytochrome bc1 complex and some of its constituent polypeptides from bakers yeast and have studied its spectroscopy, electrophoresis and amino acid analysis. The isolated complex contained 6 mumol of b heme and approximately 3 mumol of c1 heme per g of protein. The electron paramagnetic resonance spectrum was similar to that of the beef-heart preparation. The complex consisted of 7 polypeptides with mobilities on sodium dodecylsulphate polyacrylamide gel electrophoresis corresponding to Mr 44,000, 40,000, 32,000, 32,000, 17,000, 14,000 and 11,000. One of the polypeptides with Mr 32,000 was identified on sodium dodecylsulphate gels as cytochrome c1 by porphyrin fluorescence. Cytochrome b was isolated from the complex by treating it with guanidine hydrochloride; it had a purity of 20 mumol per g of protein and consisted of a polypeptide with Mr 32,000 plus two minor bands with Mr 14,000 and 11,000. We have isolated the polypeptide of Mr 32,000 from cytochrome b and the polypeptides of Mr 44,000 and 40,000 ("core proteins") from the complex, both by preparative sodium dodecylsulphate gel electrophoresis and determined their amino acid composition. Only the b polypeptide of Mr 32,000 shows the low proportion of polar amino acid residues that is considered typical of membrane proteins.

Structural studies on a glycoprotein isolated from alveoli of patients with alveolar proteinosis

A major glycoprotein 36 000 molecular weight) has been isolated from lung lavage of patients with alveolar proteinosis and found to contain five residues of hydroxyproline, fifty residues of glycine, three residues of methionine, 3 mol of sialic acid, 4.4 mol of mannose, 4.0 mol of galactose, 6.0 mol of glucosamine, and 1 mol of fucose. Cyanogen bromide (CNBr) treatment of the glycoprotein resulted, as expected, in four peptides of apparent molecular weights of 18 000, 12 000, 5000 and 1000, respectively. The chemical compositions of the CNBr peptides indicate the presence of hydroxyproline and high amounts of glycine in all but one of the peptides; two of the four CNBr peptides contain carbohydrate. Gel filtration, acrylamide gel electrophoresis and end-group analyses of the native glycoprotein and its CNBr peptides indicate that the peptides are homogeneous. End-group analyses of the CNBr cleavage products assign the 18 000 molecular weight peptide to the NH2-terminal portion and the 1000 molecular weight peptide to the COOH-terminal portion of the native glycoprotein molecule. Pronase digestion of the 36 000 molecular weight glycoprotein, followed by gel filtration and cation exchange chromatography, resulted in two fractions. One fraction was acidic and contained all the carbohydrate, a high content of aspartic acid and no hydroxyproline. The other fraction was basic and contained 8.4% hydroxyproline, 14% proline, 28% glycine and no carbohydrate, suggesting the presence of collagen-like sequence in the peptide chain. Paper electrophoresis of the basic fraction demonstrated two components, the amino acid compositions of which are identical to those of collagen. Partial amino-terminal sequence analysis of one of the CNBr peptides (18 000 molecular weight) indicated the presence of -Fly-Pro-HyP-Gly-sequence in the peptide chain, which confirms our suggestion that collagen-like regions are present in the native glycoprotein molecule. Limited acid hydrolysis of the acidic fraction and subsequent fractionation of the acid hydrolysate using Dowex column yielded a fraction which produced brown colour with ninhydrin reagent. Paper chromatography of this fraction demonstrated a large component which also stained brown with ninhydrin reagent. After acid hydrolysis, this component was found to consist of equal amounts of asparitic acid and glucosamine, indicating that the N-acetylglucosamine of the oligosaccharides is linked to the asparagine residue of the peptide. No serine or threonine linkages are present.

Two IgM paraproteins differing in carbohydrate content in a patient with Waldenström's macroglobulinemia

Two IgM paraproteins of different electrophoretic mobility were detected in the serum of a patient with Waldenstrom's disease. Both were type kappa, existed as high molecular weight polymers, and contained J-chain. The faster-moving protein contained a greater amount of carbohydrate, in both H and L chains.

A screening method to detect clonal secretion of DNP-specific antibody

Spontaneous variants of the IgA immunoglobulin secreting mouse myeloma, S194-2, were isolated by cloning the line on soft agar and screening for the loss of secreted S194 immunoglobulin. Because S194 IgA possesses DNP binding activity, the screening method was designed to test for clonal secretion of antibody which specifically precipitated DNP-ferritin conjugates. Precipitates formed over IgA secreting S194 clones, whereas none were evident over nonsecreting XCl clones nor IgG secreting MOPC 21 clones (MOPC 21 IgG does not bind DNP). In addition the method was sensitive to the amount of immunoglobulin secreted. By continual selection of exceptionally reactive clones with this assay, a S194 culture was obtained which secreted five to six times as much IgA as the original mass culture. Spontaneous variants were isolated from six independent subclones of this parent line with an overall frequency estimated at 2.7 X 10(-5) per cell per generation. Biochemical analysis of these variants showed that all of them secreted reduced or undetectable amounts of IgA. No variants were obtained which secreted IgA molecules altered at the DNP binding site, or which secreted immunoglobulin subunits alone. Variants of the latter class have, however, been obtained in high frequency in other myeloma strains by other investigators.

Isolation and characterization of two hydroxyproline-containing glycoproteins from normal animal lung lavage and lamellar bodies

Two glycopeptides, present in particulate material obtained by pulmonary lavage from normal rabbits, were isolated and characterized. The same two glycopeptides were present in preparations of lamellar bodies from rabbit lung. The estimated molecular weights of the two glycopeptides by sodium dodecyl sulfate-acrylamide gel electrophoresis were found to be 62,000 and 36,000 and both were found to contain hydroxyproline and relatively high amount of glycine (11 and 15 per cent, respectively). Carbohydrate analysis of the two glycopeptides demonstrated the presence of glucosamine, sialic acid, mannose, Fucose, and galactose. Similar glycopeptides of the same molecular weights, and amino acid and carbohydrate compositions have been found in layage mateial isolated from lungs of patients with alveolar proteinosis. The data indicate that thses two collagen-like glycopeptides are major intra-alveolar proteins in many mammals, including humans.

Studies on the structure and activity of rabbit Clq (a subcomponent of the first component of complement)

1. The subunit structure of rabbit subcomponent C1q was examined in a previous publication (Reid et al., 1972). The present paper describes some aspects of the structure of the polypeptide chains derived from the molecule. 2. The three polypeptide chains, produced by performic oxidation, of rabbit subcomponent C1q were isolated by ion-exchange chromatography in 8m-urea on DEAE-cellulose. 3. Each chain was found to contain 15-18% glycine and significant amounts of the amino acids hydroxyproline and hydroxylysine. 4. By means of collagenase digestion it was shown that all three chains of rabbit subcomponent C1q contain collagen-like sequences of amino acids which constitute about 40% of each chain. 5. By use of carboxypeptidase A it was established, indirectly, that the collagen-like sequences, in one of the chains, are probably located near, or at, the N-terminal end of the chain. 6. Collagenase digestion and heating at 52 degrees C (but not at 49 degrees C) caused rapid loss of native rabbit subcomponent C1q haemolytic activity.

Isolation and characterization of the components of the sodium pump

A satisfactory understanding of the functions of the sodium pump, the system responsible for the active transport of sodium and potassium, require the isolation and characterization of its protein and lipid components which are integrated in the structure of the cell membrane. The enzyme system (Na++ K+)-ATPase, is located in membrane fragments and behaves in the test tube like the transport system in the intact cell membrane (Skou,1957) Purified preparations of this enzyme will contain some, if not all, of the components of the sodium pump.

Characterization of a unique muscle cell line

A clonal cell line derived from a mouse neoplasm is described which shares many properties with smooth muscle. The cells have electrically excitable membranes capable of generating overshooting action potentials, and they contract both spontaneously and with electrical stimulation. They respond to the iontophoretic application of acetylcholine with a depolarizing response, and to norepinephrine with a hyperpolarizing response. Electron microscopy reveals that the cells have a morphology similar in many, but not all, respects to that of smooth muscle cells in vivo. The cells secrete soluble collagen-like molecules in addition to several proteins of undefined function. Finally, there is an increase in the specific activities of creatine phosphokinase and myokinase associated with increased cell density and the cessation of cell division.