William G. Gordon

Photoöxidation of amino acids in the presence of methylene blue

Abstract A systematic study was made of the photochemical action of methylene blue on amino acids. Tyrosine, tryptophan, histidine, methionine, and cystine were highly reactive during the photooxidation; the rest of the amino acids acted sluggishly or not at all. In tyrosine, tryptophan, and histidine, the entire oxygen uptake and CO 2 evolution were due to the cyclic nucleus, involving rupture of the rings. During the photochemical action of methylene blue on tyrosine, tryptophan, and methionine, intermediary oxidizing agents were formed; in methionine this was shown to be H 2 O 2 . The photooxidation of methionine resulted in the formation of methionine sulfoxide as an end product. Iodometric titration and measurement of ultraviolet absorption during irradiation of methionine indicate the formation of an intermediary dehydrogenation product which appears to differ from Lavines dehydromethionine. Cystine was photooxidized, probably beyond the cysteic acid stage. Peptide bonds did not participate in the photochemical action of methylene blue. Methylation of the α-amino group of lysine to the corresponding secondary and tertiary compounds produced increased reactivity in the photooxidation.

The major component of human casein: A protein phosphorylated at different levels

Abstract A single protein, with 0–5 atoms of P per molecule, makes up the major portion of human casein. Also present is a fraction similar to bovine kappa-casein in its ability, in the presence of Ca2+, to solubilize the phosphoprotein us micelles.

Amino acid composition of crystalline α-lactalbumin

Abstract The amino acid composition of α-lactalbumin has been determined by chromatography on Dowex 50 resin. Outstanding features of its composition are high content of aspartic acid and tryptophan and low content of arginine, methionine, and proline. The analytical results yield a molecular weight of 15,500, in good agreement with physical measurements. The recovery of serine and threonine from α-lactalbumin hydrolyzates remains constant with increasing time of hydrolysis.

Preparation of β- and γ-caseins by column chromatography

Abstract A new method for preparing β- and γ-casein is described consisting of fractionation of that portion of casein which is soluble at pH 4 at 2° followed by chromatography on ion-exchange cellulose. The homogeneity of the preparations is evaluated by means of starch-gel electrophoresis in the presence of urea.

Evidence from amino acid analysis for a relationship in the biosynthesis of γ- and β-caseins

Abstract γ-Casein, like β-casein, is polymorphic as shown by gel electrophoresis. Two variants of γ-casein, A 2 and B, have been isolated from samples of bovine casein genetically typed β-casein A 2 and B. The β-caseins were also isolated from the same samples. By comparison of the composition of the proteins it was shown that γ -A 2 differs from γ-B only in content of single residues of four amino acids and two substitutions, Ser/Arg and His/Pro are postulated. β -A 2 differs from β-B in the same manner, implying a close relationship in the synthesis of these milk proteins. The γ-caseins differ considerably from the β-caseins in content of proline and phosphorus. Comparison of the composition of four polymorphs of β-casein indicated that, in addition to the Ser/Arg and His/Pro substitutions, a third, Glu/Lys, may occur in the β-casein variants.

Amino acid composition of α1-, α2-, and α3-caseins

Abstract Amino acid analyses have been made of a purified α-casein, of its principal component, α 1 -casein, and of two other purified components, α 2 - and α 3 -caseins. α 1 -Casein resembles α-casein in content of most amino acids, but both differ from α 2 - and α 3 -caseins which have their own characteristic amino acid compositions.

The isolation and amino acid composition of two peptides from chymotryptic digests of β-lactoglobulins A and B

Abstract Short-term chymotryptic digests have been carried out with β-lactoglobulins A and B, performic acid-oxidized and S-sulfonated derivatives. Differences in the peptide patterns have been found after high-voltage electrophoresis only when disulfide bonds were previously cleaved. Two peptides have been isolated from chymotryptic digests of S-sulfonated β-lactoglobulins, and their amino acid compositions have been determined to be as follows: For the peptide from the β-A derivative: Asp 2 , Thr 1 , Glu 4 , Pro 1 , Ala 3 , Val 1 , Ileu 2 , Phe 1 , 1 2 Cys 1 , Lys 4 ; and for the peptide from β-B: Asp 1 , Thr 1 , Glu 4 , Pro 1 , Ala 3 , Val 1 , Ileu 2 , Phe 1 , 1 2 Cys 1 , Lys 4 , Gly 1 . The sole difference lies in the aspartic acid-glycine content. The valine-alanine difference in β-lactoglobulins A and B remains unaccounted for in the present study.

Effects of modification of ε-amino groups on the interaction of κ- and αs1-caseins

Abstract 1. 1.|The reaction of κ-casein B and α s 1 - casein C with formaldehyde suggested that their free amino groups might be essential for their native functions. Other amino group-modifying reagents were then employed since the specificity of formaldehyde is doubtful. 2. 2.|The capacity of κ-casein B for stabilizing α s 1 - casein C in the presence of Ca2+ is abruptly abolished after five of its nine positively charged lysine residues per molecule (monomer mol. wt., 19 000) are converted to uncharged homocitrulline residues by carbamylation. A marked decrease in sedimentation coefficient at 1% protein concentration coincided with the loss of protective colloid function of carbamylated κ-casein B. These findings indicate that changes in conformation and/or aggregation of κ-casein B occur due to the increase in net negative charge that accompanied carbamylation of the fifth lysine residue per molecule. 3. 3.|In other experiments the lysine residues of κ- and α s - caseins were converted to homoarginine, e-N,N- dimethyllysine and e-N- isopropyllysine residues. Such modification retains the charges of the lysine residues while sterically hindering their e-amino groups. Since the native properties of the κ-casein B and α s 1 - casein C were conserved, it seems doubtful that a specific e-amino group is critically involved in the interaction of these proteins.

Chemistry of Allergens

Twelve new antigens previously have been demonstrated in the pepsin digests of milk proteins. The term ‘new antigen’ is defined as an antigen with a specificity distinct from that of the protein from which it was generated. Three new antigenic (α-, β-, and D2i) polypeptides and one nonantigenic γ-polypeptide have been isolated from the dialysates of six successive pepsin hydrolyses of β-lactoglobulin. The α- and β-ρolypeptides were 1/5 and D2i was 1/10–1/20 as potent immunogens as precursor β-lactoglobulin as determined by the Schultz-Dale technique. The minimum observed amounts of new antigen eliciting maximum response of uterine strips in the Schultz-Dale tests were: α-D2, 50 ng; β-D2, 15 ng; β-D3, 10 ng; and D2i, 1,000 ng. Except for the α-polypeptide, the amino acid contents of the polypeptides differed markedly from that of β-lactoglobulin. The β-polypeptide has been tentatively identified as a 33 amino acid fragment of β-lactoglobulin (3,910 daltons). The γ-polypeptide has been tentatively identified as a 12 amino acid fragment of β-lactoglobulin (1,372 daltons).

Amino acid composition of β-caseins from the milks of Bos indicus and Bos taurus cows: A comparative study

Abstract 1. 1. β-Caseins B ( Bos taurus ), B Z and D ( Bos indicus ) were examined for amino acid composition. 2. 2. B Z differs from B in content of several neutral amino acids and possibly glutamic acid, as well as in tryptic “fingerprints”. 3. 3. β-D differs from B Z notably in content of arginine (+1), lysine (+1) and histidine (−1), but also in one additional residue each of threonine, serine and alanine. 4. 4. β-D (like β-C, Bos taurus ) lacks 1–2 residues of phosphorus as compared with B. 5. 5. It is likely that β-C ( Bos taurus ), itself, occurs as polymorphs.