INHIBITION OF CAMEL LENS ZETA-CRYSTALLIN NADPH-QUINONE OXIDOREDUCTASEACTIVITY BY CIBACRON BLUE/

Camel lens zeta-crystallin/NADPH:quinone oxidoreductase activity was i nhibited by Cibacron blue 3GA (CB) with 9,10-phenanthrenequinone (PQ) as an electron acceptor and NADPH as an electron donor in a time-indep endent and concentration dependent manner. The IC50 value of CB was 50 nM. The Lineweaver-Burk plots and the secondary plots indicated that the inhibition was linear mixed type (partial competitive and pure non competitive) with respect to NADPH and noncompetitive with respect to PQ. The estimated inhibition constant (K-i) values were 26.0 nM for NA DPH and 55.0 nM for PQ respectively, suggesting that CB has high affin ity towards the NADPH binding site. The secondary plots of inhibition with respect to NADPH, also indicate a dissociation constant (K-l) val ue of 68.0 nM for the zeta-crystallin-NADPH-CB complex. This K-l bring greater than the K-i value suggests that noncompetitive inhibition is predominant over competitive inhibition at the NADPH binding site.