Gamma Glutamyl Peptidase: A Novel Enzyme From Hairless Mouse Epidermis

Abstract Recent literature has suggested that pyroglutamate (PCA) formation in stratum corneum occurs by spontaneous cyclization of glutamine residues derived from filaggrin breakdown. This paper describes an enzymatic alternative. Epidermal homogenates from hairless mice were found to catalyze the formation of PCA from both glutamine and glutamic acid at pH 6.2. Enzyme activity responsible for the first step in this reaction, γ-glutamyl peptide formation, was partially purified using ammonium sulfate precipitation followed by ion exchange, gel filtration, and hydroxylapatite chromatography. Enzyme preparations free of γ-glutamyl cyclotransferase activity (which forms PCA from certain γ-glutamyl peptides) catalyzed formation of γ-glutamyl-glutamine from glutamine and γ-glutamyl-glutamate from glutamic acid. Enzyme preparations catalyzed hydrolysis of a variety of γ-glutamyl peptides but did not split non-γ-glutamyl peptides or the transpeptidase substrate γ-glutamyl-ρ-nitroanilide. Ammonium sulfate fractions containing both γ-glutamyl peptidase and γ-glutamyl cyclotransferase activity catalyzed linear formation of PCA from glutamic acid for periods of up to 19 h. Using γ-glutamyl-leucine as a substrate, γ-glutamyl peptidase activity was found to be much higher in crude extracts from epidermis than in preparations from liver, kidney, spleen, intestine, lung, brain, or heart. This activity has not, to our knowledge, been previously described in mammalian tissues.