Glycyl-glycine hydrolase of rat brain: Distribution and role in cleavage of glycine-rich oligopeptides

Abstract

STERN, F. AND N. MARKS. Glycyl-glycine hydrolase of rat brain: Distribution and role in cleavage of glycine-rich oligopeptides. BRAIN RES. BULL. 4(1) 49–55, 1979.—The specificity and distribution of glycyl-glycine hydrolase (E.C.3.4.13.1) were studied in rat brain by several analytical procedures. Compared to other dipeptides Gly-Gly was unique in terms of its activation by Co 2+, which had no effect on other substrates or inhibited their breakdown. Gly-Gly was cleaved at a rate of 180 μmoles per g wet wt. per hr in the absence of Co 2+. It rose 4-fold on addition of Co 2+, and 2-fold with Mn 2+; it is thus comparable in rate to many other exopeptidases. Its pH optimum was 7.9 with an apparent K m of 4.3 in the absence of metal ion, and 2.7 in its presence. For glycine-rich tri- and oligopeptides, activation by metal ion occurred only with substrates yielding Gly-Gly as an intermediate (Gly-Gly-Gly, Leu-Gly-Gly, enkephalin, delta sleep inducing peptide). Activity was highest in striatum and cerebellum and lowest in spinal cord and pituitary. In subcellular fractions over 40% of the activity was present in the cytosol, with lesser amounts in the debris, nuclear and mitochondria! fractions. Activity increased during development, reaching maximum values during myelination. The enzyme was partially purified by CM-cellulose chromatography or isoelectric focusing; it was stable when stored at −70°C. Crude and partially purified enzymes were inhibited by Zn 2+, Ni 2+, Fe 2+, a number of sulfhydryl reagents, and EDTA. Enzyme activity in vitro greatly exceeded that required to degrade Gly-Gly generated as a result of normal protein turnover and may account for the absence of this dipeptide in soluble extracts.