Inhibition of rat liver asparagine synthetase by Cibacron Blue F3GA.

Cibacron Blue F3GA, a blue chromophore of Blue Dextran, inhibited the activity of rat liver asparagine synthetase uncompetitively with respect to glutamine (Kii = 7.8 mumol/l), competitively with respect to aspartate (Kis = 3.1 mumol/l) and noncompetitively with respect to ATP (Kii and Kis = 5.0 mumol/l). The inhibitions were linear against the dye concentrations. These results are compatible with the postulate that asparagine synthetase reaction proceeds through a ping pong mechanism in which glutamine is bound first, followed by glutamate release, and then aspartate and ATP is bound in order. The experiments demonstrate that the dye could be useful in analyzing the kinetic mechanism of asparagine synthetase.