THE BINDING AND CONJUGATING ABILITIES OF THE Y-FRACTION FOR SULFOBROMOPHTHALEIN (BSP) IN CHRONIC CARBON TETRACHLORIDE-INTOXICATED RATS

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It was revealed by the Sephadex G-75 gel filtration of rat liver supernatant containing sulfobromophthalein (BSP) that the rats chronically intoxicated with CCl_4 have lower BSP conjugating activities as well as lower protein contents in the Y-fraction than the control rats. Enzyme kinetic studies on the Y-fraction were carried out in order to investigate the changes induced by intoxication in the properties of glutathione S-transferases in the Y-fraction with BSP as a substrate. Since neither K_m (Michaelis-Menten constant) nor V_<max> (maximum velocity) value changed, no alteration by the intoxication was observed in the Y-fraction as a conjugating enzyme. It is clear that the intoxication brought about a decrease in the enzyme content in the Y-fraction, considering that protein concentration of the Y-fraction on the gel filtration decreased without the change of V_<max> value. Our previous report showed that the content of endogeneous glutathione (GSH) was not altered by the intoxication. These observation led to the conclusion that the decreased BSP conjugating activity by the intoxication was due to the decreased content of enzyme in the Y-fraction. The BSP binding to the Y-fraction was measured by equilibrium dialysis. It was found that the intoxication reduced the binding constant by more than 50%, whereas the change of dissociation constant (K_m) estimated from the enzyme kinetics was not observed.
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