Eukaryotic TGs evolved from the papains, but utilizing a Trp/ Cys/His/Asp catalytic tetrad instead of Gln/Cys/His/Asp for acy-lation-deacylation. Because saturable binding of specific amine substrates, aminolysis is preferred over hydrolysis in deacylation. Transamidation leads to protein remodelling of the gamma amides of select Gln residues by crosslinking to epsilon amines of select Lys’s or by incorporation of small primary amines. Such post-translational modifications have important biological conse-quences. .
