The formation of basic amino acids on treatment of proteins with alkali

Effects of alkali on proteins. Disulfides and their products

“…The results of amino acid analysis of alkali-treated lysozyme and «-lactalbumin (2 X 10™4 M in 0.1 M NaOH at 50 °C) have shown that for each mole of protein, 1 mol of lanthionine (half meso-and half dl-), 5 mol of lysinoalanine, and 1 mol of /8-aminoalanine are formed at the end of 24 h. This was accompanied by the complete loss of all four cystines and five lysines. Asquith et al (1969) have reported the formation of lysinoalanine and ßaminoalanine upon alkali treatment of lysozyme, but did not report formation of lanthionirie. Sulfur and hydrogen sulfide analyses of alkali-treated lysozyme (2 X 10~4 M in 0.1 M NaOH at 50 °C) indicated that for each mole of protein, 3 mol of hydrogen sulfide and 4 mol of sulfur are formed after 24 h. The presence of free sulfur, which has long been known to be formed (Mulder, 1838), cannot be accounted for by either the hydrolysis or «-elimination mechanisms.…”

“…Danehy and Parameswaran (1968) have shown that the alkaline decomposition of ten aromatic disulfides follows the generalization of Parker and Kharasch (1960) that the disulfide which gives rise to a more stable anion should decompose more rapidly than the one that gives a less stable anion. Although evidence in support of the ß- e-Aminoalanine (s-AAL) (Asquith et al, 1969) Lanthlonine (LANTH) (Horn et al, 1941) Figure 9. Possible products that may form through nucleophilic addition (Michael-type addition) to a dehydroalanine intermediate in alkali-treated proteins.…”

Aspects of the formation of lysinoalanine in milk and milk products

“…Products of addition reactions between dehydroalanine and the <?-amino group of ornithine which can be formed from arginine by alkali treatment as demonstrated by Ziegler et al (1967) or with the thiol group of cysteine (Corfield et al 1967;Asquith & Garcia-Dominguez, 1968) lead to the formation of ornithinoalanine and lanthionine respectively. Asquith et al (1969) reported that /?-aminoalanine was probably derived from the reaction of ammonia with dehydroalanine. These reactions are summarized in Fig.…”

Damage to nutritional value of plant proteins by chemical reactions during storage and processing

“…It is worth mentioning some of the known chemical effects of alkali on proteins: (I) Racemization and epimerization of amino acid residues, especially those in peptide linkage, as demonstrated, more than fifty years ago, by Abderhalden, Dakin and Levene. This results in unsusceptibility of peptide bonds to proteases, as well as in possible toxicity of the D-amino acids, amino acid diastereoisomers and oligopeptides in which such residues are present; (II) Conversion of arginine to citrulline and ornithine residues; (III) Conversion of cyst(e)ine residues to 0~-aminoacrylic acid residues, leading to further reactions with lysine e-amino groups to give lysinoalanine, with ornithine 6-amino groups to give ornithinoalanine, with cyst(e)ine residues to give lanthionine and with ammonia or amide residues to give a/3-diaminopropionic acid (Ziegler, Melchert & Ltirken, 1967;Asquith & Garcfa-Domfnguez, 1968, a, b;Asquith, Booth & Skinner, 1969;Asquith & Carthew, 1972, a, b;Jocelyn, 1972;Asquith, Carthew, Hanna & Otterburn, 1974;Otterburn, 1975)(see also Abbott, Asquith, Chan & Otterburn, 1975;Asquith, Hanna & Otterburn, 1975). Serine residues can react in the same way (Robson & Zaidi, 1967;Ziegler, Metchert & Liirken, 1967;Asquith, Booth & Skinner, 1969).…”