. "\"The formation of a 2-keto-5-iminopiperazine protein chromophore cross-link from the alpha-amino nitrogen of residue n, a methionine, to the alpha-carboxyl carbon of residue n+1, a tyrosine, and a dehydration to form a double bond to the alpha-amino nitrogen of residue n+2. This cross-linking is coupled with a dehydrogenation of residue n+1 to form a double bond between the alpha and beta carbons.\" [PMID:10852900, PMID:11259412, PMID:15491166, RESID:AA0377]" . . "peptide cross-linking via 3-(2-methylthio)ethyl-6-(4-hydroxybenzylidene)-5-iminopiperazin-2-one" . "biosynthesis of protein-protein cross-link via L-methionyl-L-tyrosyl-2-keto-5-iminopiperazine" . "biosynthetic process of protein-protein cross-link via L-methionyl-L-tyrosyl-2-keto-5-iminopiperazine" . "RESID:AA0377" . "Note that this predicted modification is now thought not to exist. See the biological process term 'peptide cross-linking via 2-imino-methionine 5-imidazolinone glycine ; GO:0051359'." . . . . .