Camel lens zeta-crystallin kinetics and its inhibition by dicoumarol

zeta-Crystallin a novel NADPH quinone oxidoreductase of the camel lens is capable of reducing a non quinone compound such as 2,6-dichlorophenolindophenol (DCIP) which is mediated by NADPH. A classical Michaelis-Menten kinetics were exhibited for both DCIP and NADPH with Km values of 15.3 microM and 7.0 microM respectively, at pH 7.8. The Vmax was 1.60 mumol./min.mg protein. The results of steady-state kinetic analysis indicated that the reaction proceeds through a Ping-Pong mechanism. Dicoumarol was found to be a competitive inhibitor of zeta-crystallin with respect to DCIP with a Ki value of 14.6 microM and showed uncompetitive inhibition with respect to NADPH with a Ki value of 36.2 microM.