Some properties of glutamine synthetase from the nitrifying bacterium nitrosomonas euro paea

Abstract

Nitrosomonas europaea oxidizes ammonia to nitrite, thereby deriving energy for growth. Glutamate dehydrogenase (NADP+) (EC 1.4.1.4) is the main route for the incorporation of ammonia into glutamic acid, because glutamate synthase (NADPH) (EC 1.4.1.13) was not detected in cell-free extracts of N. europaea. Some properties of a partially purified glutamine synthetase (EC 6.3.1.2) have been determined, namely the effects of pH and metal ions, substrate requirements, Km and Ki values, based on biosynthetic and y-glutamyltransferase (EC 2.3.2.2) assays. The molecular.weight of the enzyme preparation was approximately 440000. The y-glutamlytransferase activity was markedly inhibited by alanine, lysine, glutamic acid, aspartic acid and serine and to a lesser extent by glycine, asparagine, arginine and histidine. Except for tryptophan and cystine, the γ-glutamlytransferase activity was inhibited to a greater extent by these amino acids than was the biosynthetic activity. Different pairs of amino acids in various combinations resulted in a cumulative inhibition of enzyme activity determined by either method. Of the various nuc1eotides tested, the γ-glutamlytransferase activity of the enzyme was inhibited to a greater extent by di- and triphosphate nuc1eotides-IDP, CDP, UDP, ITP, CTP, TTP and ATP (except GDP and GTP) than by monophosphate nuc1eotides except AMP. Saturating concentrations of pyruvate, oxalate, oxaloacetate and α-ketoglutarate depressed enzyme activity. Various combinations of amino acids with adenine nuc1eotides exerted cumulative inhibitory effects on the transferase activity. © 1981 ASEG.