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This enzyme is the first glutamine amidotransferase that participates in the anaerobic (early cobalt insertion) biosynthetic pathway of adenosylcobalamin, and catalyses the ATP-dependent synthesis of cobyrinate?a,c-diamide from cobyrinate using either?L-glutamine or ammonia as the nitrogen source. It is proposed that the enzyme first catalyses the amidation of the?c-carboxylate, and then the intermediate is released into solution and binds to the same catalytic site for the amidation of the?a-carboxylate. The?Km?for ammonia is substantially higher than that for?L-glutamine. |
