Study of the dansylation reaction of amino acids, peptides and proteins

Structural studies on bovine -crystallin

The amino acid sequences around the cysteine residues in the lens protein, gamma-crystallin, were studied. Fraction II of the gamma-crystallin from calf lens (Björk, 1964) was used. The protein was oxidized with performic acid and then hydrolysed with trypsin. Six peptides containing cysteic acid were isolated. One of the peptides contained three residues of cysteic acid and the others contained one residue of cysteic acid. We conclude that there are eight unique residues of cysteic acid in the oxidized protein. Amino acid analysis suggests that there are also eight residues of cysteic acid in the molecule, which thus contains only one polypeptide chain.

Bovine pepsinogens and pepsins. A series of zymogens and enzymes that differ in organic phosphate content

Several minor pepsinogens, present in extracts of bovine fundic mucosa obtained from the fourth stomach or abomasum, were separated from the main pepsinogen by chromatography on hydroxyapatite at pH7.3. The major pepsinogen and two of these minor pepsinogens were studied in detail. All three zymogens have N-terminal Ser-Val-, C-terminal -Val-Ala and not more than 1mol of glucose/mol of protein; no significant differences in amino acid composition were found. The pepsinogens differ in their organic phosphate content, which accounts for their chromatographic separation. By activation at 0 degrees C and pH2, a corresponding series of pepsins is formed. These enzymes were separated by hydroxyapatite chromatography at pH5.7. All the pepsins have N-terminal valine, C-terminal alanine and are free from carbohydrate. Again the only difference detected among them is in their organic phosphate content. The pepsins of high phosphate content are converted by an acid phosphatase in vitro into pepsins of low phosphate content.

A lipoprotein characterizing obstructive jaundice. II. Isolation and partial characterization of the protein moieties of low density lipoproteins

The plasma low density lipoproteins (LDL) in biliary obstruction are characterized almost exclusively by the presence of the immunochemically distinct lipoprotein families, lipoprotein B (LP-B) and lipoprotein X (LP-X). It is suggested that LP-X, with its uniquely high content of unesterified cholesterol and phospholipid, is primarily responsible for the unusual lipid composition of LDL and the abnormal plasma lipid composition in obstructive jaundice. To show their protein moieties, we isolated LP-X and LP-B from the LDL in plasma obtained from patients with obstructive jaundice. A separation procedure was employed which combines ultracentrifugation, heparin precipitation, and ethanol fractionation. Whereas LP-B was characterized by the presence of apolipoprotein B (ApoB), intact LP-X contained a protein moiety of unique composition consisting of a mixture of albumin (approximately 40%) and the specific apolipoprotein, ApoX (60%). These two protein moieties were separated by preparative ultracentrifugation at d 1.21 g/ml of a solution of partially delipidized LP-X. LP-X thus comprises an albumin-lipoprotein complex in which the masked antigenic site of albumin can be revealed by partial or total delipidization. Apolipoprotein X, the characteristic nonalbumin protein moiety of intact or partially delipidized LP-X, was immunochemically different from ApoA, ApoB, albumin, gamma-globulins, and other serum proteins. The results of analytical ultracentrifugation and the immunochemical and electrophoretic properties of ApoX indicated it to be a complex protein consisting possibly of several nonidentical polypeptides. ApoX was characterized by its amino acid composition, and by serine and threonine as the major N-terminal and alanine as the major C-terminal amino acids. It has been suggested that ApoX is similar to, if not identical with, apolipoprotein C.

Purification and amino acid sequence of melanocyte-stimulating hormone from the dogfish Squalus acanthias

A melanocyte-stimulating hormone (MSH) was isolated by gel filtration and ion-exchange chromatography from extracts of the pituitary glands of dogfish. Sequence studies were carried out on the hormone and its enzymically and chemically cleaved fragments. The sequence of the hormone, Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Met, shows that ten of its 11 residues are the same as ten of the 13 residues of mammalian alpha-MSH. About half of its molecules have the carboxyl group at the C-terminus free and about half are amidated; about a fifth have an extra tyrosine residue on the N-terminus, thereby making 11 residues the same as in mammalian alpha-MSH. Unlike the mammalian hormone, however, none of it was found to be N-acetylated.

A variable region subclass of heavy chains common to immunoglobulins G, A, and M and characterized by an unblocked amino-terminal residue

Heavy chains of IgG, IgA, and IgM classes of human immunoglobulins were compared by N-terminal residue determination and partial amino acid sequence analysis. A third subclass of the variable region of heavy chains was observed; an unblocked glutamic acid as the N-terminal residue is characteristic of this subclass. Our results indicated that the heavy chain variable region subclasses are not class specific, and that a given heavy chain variable region may be found in association with constant regions for mu-chains, alpha-chains, or gamma-chains of various subclasses.

The amino acid sequence of Phaseolus aureua L. (mung-bean) cytochrome c

The amino acid sequence of Phaseolus aureus L. (mung-bean) cytochrome c has been determined. The molecule consists of a single polypeptide chain of 111 amino acid residues and is homologous with other mitochondrial cytochromes c. Comparison with the amino acid sequence of wheat-germ cytochrome c (Stevens, Glazer & Smith, 1967) shows 14 differences. On alignment with mammalian cytochromes c, mung-bean cytochrome c has an N-acetylated ;tail' of eight amino acid residues similar to that found in wheat-germ cytochrome c. Of the 22 positions in wheat-germ cytochrome c that contain amino acid residues unique to these positions, 20 were found to contain the same ones in mung-bean cytochrome c. The in-N-trimethyl-lysine residues reported for wheat-germ cytochrome c (Delange, Glazer & Smith, 1969) in positions 72 and 86 were also found in these positions in mung-bean cytochrome c. The sequence was determined from 3mumol, by using chymotryptic and tryptic peptides which were analysed by the ;dansyl'-Edman method (Gray & Hartley, 1963a), with confirmation by amino acid analysis.

Transcarboxylase. 8. Isolation and properties of a biotin-carboxyl carrier protein

Methylmalonyl CoA-oxalacetate transcarboxylase (EC 2. 1. 3. 1) from Propionibacterium shermanii is a biotin enzyme of 670,000 molecular weight containing 6 moles of biotin per mole of enzyme. The active enzyme dissociates spontaneously at low ionic strength and alkaline pH to a mixture of inactive subunits. One type of subunit contains all the biotin of the original molecule. The biotin unit has an S(20,w) = 1.3S and a molecular weight of approximately 12,000. It contains 1 mole of biotin and 1 half-cystine per mole. Qualitative dansyl techniques indicate that alanine is the amino terminal residue of the biotin subunit.