γ-Glutamyl Transfer Reactions

Abstract

This chapter discusses γ-glutamyl transfer reactions. There are enzymatic potencies widely distributed in nature that catalyze the transfer of the glutamyl radical of glutamine to other amines and that of glutamyl peptides to other amino acids or peptides. It cannot be decided at present whether these enzymes catalyzing the transfer of the γ-glutamyl radical are specific or whether this activity is an expression of the broad specificity of proteinases catalyzing transpeptidation reactions. The significance of different transfer reactions involving γ-glutamyl radical were first interpreted as the utilization for peptide bond formation of phosphate bond energy through glutamine and glutathione, which are synthesized from the respective building stones with the participation of ATP. The γ-glutamyl group was, therefore, considered as the biological analogue of the carbobenzyloxy group. The outstanding biological representative of γ -glutamyl peptides in nature is glutathione (GSH). If some of the transfer reactions occur during periods of active protein synthesis, one should expect γ -peptides other than GSH to be present even though in small amounts.