Glutaminase A of Escherichia coli

Glutaminase A isolated from Escherichia coli reacts with the glutamine analogue, 6-diazo-5-oxonorleucine, in two ways: (a) it catalyzes hydrolysis of the C5—C6 bond to yield glutamic acid and diazomethane; and (b) a group at the active site of the enzyme becomes irreversibly alkylated by the intact carbon chain of the analogue. The reactions are thought to occur through association of the compound with the substrate binding site followed by acid catalyzed attack of an enzyme group either at C5 to yield glutamic acid and diazomethane, or at C6, to inhibit the enzyme. The ratio of rate of hydrolysis to that of alkylation is about 70. Diazomethane was identified by observing that both the reaction product from diazo-oxo[6-14C]norleucine and [14C]diazomethane itself react with water and with benzoic acid to give labeled methanol and methyl benzoate in the same ratio.