Kinetic studies on asparagine synthetase from mung beans ( Vigna radiata (L) wilczek) with a phosphonate analogue of a proposed reaction intermadiate

Abstract

We have synthesized l-2-amino-4-oxo-5-(5′-adenosyl)phosphonopentanoic acid, II , as an analogue of aspartyl adenylate, I . This latter intermediate is proposed to occur during activities of the enzyme asparagine synthetase (glutamine hydrolysing) ( l-aspartate: l-glutamine amido-ligase (AMP forming, EC 6.3.5.4). Enzyme kinetic studies indicate that inhibition of the mung bean enzyme by II is noncompetitive with respect to glutamine and uncompetitive with respect to both ATP and aspartate, with a K i of 0.08 mM. This suggests that if II is acting as an analogue of I then the synthesis of asparagine involves the binding of I to two distinct sites on the enzyme.