Hydrolysis of proteins

Amino acid sequence homology between HLA-A,B,C antigens, beta2-microglobulin and immunoglobulins

Papain-solubilized HLA-A,B,C antigen heavy chains have been cleaved by combined acid and CNBr treatment to yield three large fragments. A 14,000-dalton peptide comprises the NH2-terminal portion of the molecule, less a five-membered peptide. The 14,000-dalton fragment is followed in the linear sequence by a 9000-dalton peptide connected through an aspartyl-prolyl bond to the COOH-terminal 11,000-dalton fragment. The 9000- and 11,000-dalton fragments contain disulphide bridges that are immunoglobulin-like inasmuch as they encompass some fifty-five to sixty amino acid residues. The NH2-terminal portion of the HLA antigen heavy chain is devoid of cysteine. NH2-terminal amino acid sequence analyses do not reveal homologies between the 14,000- and 9000-dalton fragments, beta2-microglobulin, and the constant immunoglobulin domains. However, the NH2-terminal sequence of the 11,000-dalton fragment is as homologous to beta2-microglobulin and the constant immunoglobulin domains as they are to one another.

Isoleucine Epimerization in Peptides and Proteins: Kinetic Factors and Application to Fossil Proteins

The observed rate of isoleucine epimerization in peptides and proteins is dependent on (in addition to time and temperature) (i) the position of isoleucine in the peptide chain, (ii) the nature of adjacent amino acids, and (iii) the stability of the isoleucine peptide bonds. The relative rate is: NH(2)-terminal > COOH-terminal >> interior >/= free amino acid. The gradual hydrolysis of peptides and proteins to the more slowly epimerizing free amino acid causes a decrease in the apparent first-order rate constant with time. These results explain the isoleucine kinetics observed in fossil shells.

Purification and properties of succinyl-coenzyme A-3-oxo acid coenzyme A-transferase from sheep kidney

CoA-transferase (succinyl-CoA-3-oxo acid CoA-transferase, EC 2.8.3.5) isolated from sheep kidney was purified to homogeneity. The purified enzyme has a specific activity of approx. 200 units/mg. A mol.wt. of 110000 was obtained by gel filtration on Sephadex G-200, and a lower mol.wt. of 102000 was determined by analytical ultracentrifugation. A sedimentation coefficient of 5.6S was also determined. A subunit mol.wt. of 56000 was obtained by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Isoelectric focusing of sheep kidney extracts indicated the presence of a single band of CoA-transferase activity with pI9.0. However, isoelectric focusing of purified CoA-transferase showed the presence of two peaks of CoA-transferase activity with pI values of 8.7 and 8.4, suggesting the presence of proteolytic activity during purification. Evidence for sheep kidney CoA-transferase being a dimer of two identical subunits has been obtained from sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the amino acid composition, peptide 'mapping' and N-terminal analysis.

Separation of amino acids and peptides on non-polar stationary phases by high-performance liquid chromatography

Microparticulate non-polar stationary phases, such as octadecyl-silica offer a rapid and efficient means for the separation of peptides and amino acids by high-performance liquid chromatography. Retention is attributed to hydrophobic interaction between the solutes and the hydrocarbonaceous functions covalently bound to the stationary phase surface. Consequently the species are eluted in the order of increasing hydrophobicity. Various peptide mixtures were analyzed by using gradient elution with increasing acetonitrile concentration in the eluent and monitoring the column effluent at 200 or 210 nm with an UV detector. The separation of angiotensins and enzymic digest of polypeptides illustrates the speed of the method which can be used to assay the purity of peptide hormones such as alpha-melanotropin and gramicidin or to analyze the composition of reaction mixtures involving peptides. The efficiency of the method is superior to that obtained on the conventionally used ion-exchanger columns, except for hydrophilic amino acids and peptides that are poorly retarded. Nevertheless, with a suitable ionic surfactant in the mobile phase, non-polar stationary phases can be used for the separation of these species as well.

Ion-exchange chromatographic study of amino acid degradation during hydrolysis of avian protein

The losses of amino acid during acid hydrolysis of oviduct magnum protein from the domestic fowl have been measured using a Technicon TSM-1 amino acid analyser. The results were subjected to statistical analysis and a linear regression was obtained for each amino acid investigated. Methionine, in the presence of oxygen, did not exhibit significant degradation. A loss of 5.5% was found for phenylalanine after 24 h of hydrolysis under nitrogen. It is suggested that the results could be applied to animal proteins from tissue of similar composition but not to analysis of protein from plant materials.

Determination of the structure of the novel polypeptide containing aspartic acid and arginine which is found in Cyanobacteria

The polypeptide contained in the cyanophycin granule, a characteristic cyanobacterial subcellular inclusion, is shown to be a highly branched structure consisting of a polyaspartic acid core to which arginyl residues are attached at each free carboxyl group of the polyaspartic acid. The evidence supporting such a model includes: (i) The resistance of the polypeptide to a variety of enzymatic procedures commonly used to degrade linear polypeptide chains. (ii) The inability to degrade the polypeptide from the amino terminal using sequential Edman degradation. (iii) The preferential relase of arginine following hydrolysis of the polypeptide in dilute acid (0.03 M acetic acid, 105 degrees C). (iv) The demonstration by chemical linkage analysis that both the carboxyl groups of aspartic acid are unavailable for reduction and must therefore by involved in covalent linkages and that many arginyl residues can be reduced and therefore must not be involved in covalent linkage. (v) The removal of approximately 75% of the arginine from the polypeptide by chemical treatment of the polypeptide using methods designed to cleave carboxyl-terminal amino acids. The highly branched structure of the cyanophycin granule polypeptide is similar in form to synthetically produced multichain polyamino acids, and using the nomenclature for describing multichain polyamino acids, it is proposed that the cyanophycin granule polypeptide be called multi-L-arginyl- -polyaspartic acid.

Site of hydrolysis of collagen by hot trichloroacetic acid

When calfskin collagen is treated with trichloroacetic acid at 90 degrees C, it is hydrolyzed to a mixture of peptides, some of which are quite small. Cleavage of collagen by acid seems to occur at bonds between proline (or hydroxyproline) and other amino acids, with only a limited specificity for which amino acid donates its amino group to the susceptible peptide bond.

Chemical synthesis of partially and fully phosphorylated protamines

Chromatographically purified components Z and YI of clupeine from herring have been phosphorylated by a chemical method. To enhance solubility in trimethylphosphate, the protamine capronate salts were used and phosphorylation was performed with POCl3. Both serine and threonine residues were phosphorylated; however, besides monophosphate esters considerable amounts of polyphosphate esters were obtained. Its nature was identified by 31P nuclear magnetic resonance spectroscopy and by chemical methods, such as comparison of the hydrolysis rate with that of ADP and phoshocreatine, respectively. The pyrophosphate bonds were cleaved by controlled hydrolysis with HCl. The phosphorylated protamine species were purified by gel filtration and chromatography on a Sephadex CM column. Fully phosphorylated clupeine Z (3 serine residues and 3 phosphates) and YI (3 serine, 2 threonine residues and 5 phosphates) were obtained as well as partially phosphorylated fractions; in the case of clupeine Z the resolution into mono, doubly and triply (fully) phosphorylated fractions was excellent. The overall yield of phosphorylated clupeine was better than 50%.

[Lysine resorption in rats fed on heated casein]

Male Wistar rats six month old were fed on a diet containing 10% casein heated for 4 h at 140 degrees C; control rats got untreated casein. The content of available lysine (as determined according to RAO et al.) was 5.8 g/16g N in heated and 8.5 g/16 gN in untreated casein. The contents of free and total lysine and of epsilon-DNP-lysine were estimated in deproteinized portal blood plasma and in urine. In the former the contents of the remaining amino acids before and after acid hydrolysis were also determined. Deproteinized portal blood plasma of rats fed on untreated or heated casein contained, respectively, un mumoles per 10 ml: total lysine 9.0 and 9.9; free lysine 3.7 and 2.8; bound lysine (total lysine -free lysine) 5.3 and 7.1; peptide-bound lysine (determined as epsilon-DNP-lysine) 4.9 and 4.6; and epsilon-bound lysine (bound lysine - peptide-bound lysine) 0.5 and 2.6. The data indicate that lysine with blocked epsilon-amino group was released in the course of digestion of the heated casein and absorbed. This is additionally substantiated by the presence of this form of lysine in the urine of rats given heated casein.

Specific cyanylation and cleavage at cysteine-104 human hemoglobin alpha-chain. A novel approach to the problem of the alpha-chain tryptic core in the study of haemoglobin variants by "fingerprinting" methods

1. A new approach to the analysis, by "fingerprinting", of the tryptic core region of human haemoglobin alpha-chain is described. 2. The alpha-chain is cyanylated at its single cysteine residue (alpha104) and then split, by exposure to mild alkali, at the N-peptide bond of the resulting beta-thiocyanoalanine residue. 3. The two cleavage fragments, alpha1-103 and alpha104-141, are separated by gel filtration, and the fragment alpha104-141, which contains all the residues of the alpha-chain tryptic core, is digested with pepsin. 4. Preparative "fingerprints" of these peptic peptides yield eight major peptides, which provide complete sequence information for the whole region alpha104-141. 5. The utility of the method is demonstrated by repeating the determination of the substitution in haemoglobin Hopkins-2, a known alpha-chain core variant in which histidine-alpha112 (G19) is replaced by an aspartic acid residue.

Amino acid sequence of the smaller basic protein from rat brain myelin

1. The complete amino acid sequence of the smaller basic protein from rat brain myelin was determined. This protein differs from myelin basic proteins of other species in having a deletion of a polypeptide of 40 amino acid residues from the centre of the molecule. 2. A detailed comparison is made of the constant and variable regions in a group of myelin basic proteins from six species. 3. An arginine residue in the rat protein was found to be partially methylated. The ratio of methylated to unmethylated arginine at this position differed from that found for the human basic protein. 4. Three tryptic peptides were isolated in more than one form. The differences between the two forms of each peptide are discussed in relation to the electrophoretic heterogeneity of myelin basic proteins, which is known to occur at alkaline pH values. 5. Detailed evidence for the amino acid sequence of the protein has been deposited as Supplementary Publication SUP 50029 at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.

An investigation of hydrolytic techniques for the amino acid analysis of foodstuffs

A survey of hydrolytic methods for the amino acid analysis of foods is presented and the advantages and disadvantages of the methods are discussed. Amino acids were determined after hydrolysis of the proteins with hydrochloric acid, sulphuric acid, perchloric acid, p‐toluene sulphonic acid and sodium hydroxide. The results are shown graphically using as examples a pure protein (casein) and a potential food protein of microfungal origin (Fusarium graminearum). The addition of some cation exchange resin to acids catalysed the hydrolysis of some peptide bonds containing aspartic acid, threonine, serine, glutamic acid, valine and isoleucine. Whilst several methods gave close agreement for the analysis of a pure protein, hydrolysis with 6 N‐hydrochloric acid gave the largest yield of most amino acids in food proteins. With the exception of extracted soya meal, protection of cystine prior to hydrolysis gave higher values than direct hydrolysis.

Primary structure of the ovine hypothalamic luteinizing hormone-releasing factor (LRF) (LH-hypothalamus-LRF-gas chromatography-mass spectrometry-decapeptide-Edman degradation)

The primary structure of ovine hypothalamic hypophysiotropic luteinizing hormone-releasing factor, LRF, has been established as pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH(2) by hydrolysis of the peptide with chymotrypsin or pyrrolidone-carboxylylpeptidase and by analysis of the products by an Edman-dansylation sequencing technique, as well as by mass spectrometry of the derived phenylthiohydantoins. A decapeptide with the proposed primary structure, prepared by total synthesis, gave the same result on sequencing. The synthetic decapeptide possesses the same biological activities as the native ovine LRF. The amino-acid sequence of ovine LRF is identical to that already published for porcine LRF.

Amino acid sequences around the cysteine residues of rabbit muscle triose phosphate isomerase

1. The nature of the subunits in rabbit muscle triose phosphate isomerase has been investigated. 2. Amino acid analyses show that there are five cysteine residues and two methionine residues/subunit. 3. The amino acid sequences around the cysteine residues have been determined; these account for about 75 residues. 4. Cleavage at the methionine residues with cyanogen bromide gave three fragments. 5. These results show that the subunits correspond to polypeptide chains, containing about 230 amino acid residues. The chains in triose phosphate isomerase seem to be shorter than those of other glycolytic enzymes.