New amino acid derivatives formed by alkaline treatment of proteins

Intense heat treatment of proteins at high pH favors formation of transient, reactive intermediates derived from serine and cystine. The postulated dehydroalanine intermediate reacts further with the epsilon-amino groups side chains and sulfhydryl groups of cysteine residues to form derivatives of lysinoalanine and lanthionine. Recent studies indicate that besides these crosslinked products, several others are formed, by reaction of histidine, arginine, and possibly other residues. For this reason, caution should be exercised in assigning the prelysine peak(s) of an amino acid chromatogram to lysinoalanine. These results suggest that unnatural amino acid derivatives, other than lysinoalanine, may also contribute to the toxic effects reported from studies in which alkali-treated protein was fed to rats.