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-dichloroph enolindophenol (DCIP) which is mediated by NADPH. A classical Michaeli s-Menten kinetics were exhibited for both DCIP and NADPH with K-m valu es of 15.3 mu M and 7.0 mu M respectively, at pH 7.8. The V-max was 1. 60 mu mol./min.mg protein. The results of steady-state kinetic analysi s 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 K-i value of 14.6 mu M and showed uncompet itive inhibition with respect to NADPH with a K-i value of 36.2 mu M.