Inhibition of Lysinoalanine Synthesis by Protein Acylation

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Abstract
Treating wheat gluten, soy protein, and lactalbumin under alkaline conditions at 65°C for various times destroys part of the threonine, cystine, lysine, tyrosine, and arginine residues in these proteins. The losses were accompanied by the appearance of lysinoalanine and unidentified ninhydrin-positive substances. Treating wool under samewhat milder alkaline conditions destroys part of the cystine and lysine residues, but not the other amino acids cited. In this case, loss of cystine and lysine was accompanied by the appearance of lanthionine and lysinoalanine. Amino acid analysis of alkali-treated acylated proteins revealed that acylation by acetic and succinic anhydrides prevents or minimizes destruction of lysine residues and the formation of lysinoalanine in wheat gluten and soy protein and, in wool, minimizes destruction of cystine and lysine residues and the formation of lanthionine lysinoalanine. Mechanisms are proposed to explain the observed inhibiting effects of protein acylation and certain additives on lysinoalanine formation.