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Inhibitory kinetics of betaine on β-N-Acetyl-D-glucosaminidase from prawn (litopenaeus vannamei)

Abstract:

The effects of betaine on prawn /3-W-acetyl-D-glucosaminidase (NAGase) activity for the hydrolysis of p-nitrophenyl-W-acetyl- β-D-glucosaminide (pNP-NAG) have been studied. The results showed that appropriate concentrations of betaine could lead to reversible Inhibition against NAGase, and the IC 50 value was estimated to be 15.00 ± 0.30 mM. The inhibitory kinetics assay showed that betaine was a mixed type inhibitor with a K l value of 9.17 ± 0.85 mM and a Kls value of 45.58 ± 2.52 mM. The inhibitory model was set, and the microscopic rate constants were determined using the kinetic method of the substrate reaction. The time course of the hydrolysis of pNP-NAG catalyzed by NAGase in the presence of different betaine concentrations showed that at each betaine concentration, the rate decreased with an Increase In time until a straight line was approached, indicating that the inhibition of NAGase by betaine is a slow, reversible reaction with fractional residual activity. The fact that k +0 is much larger than k+0 indicated that the free enzyme molecule is more fragile than the enzyme-substrate complex against betaine. It Is suggested that the presence of the substrate offers marked protection of NAGase against inhibition by betaine. © 2010 American Chemical Society.