消旋棉酚及其旋光异构体对小鼠乳酸脱氢酶(LDH)抑制作用的比较研究

本文用消旋棉酚及其旋光异构体比较研究了对纯化小鼠肝脏LDH-A_4,心脏LDH-B_4和睾丸LDH-C_4的抑制作用。其抑制程度与实验温度和棉酚剂量有关。37℃时的抑制作用比25℃时强得多。棉酚低浓度(1～4μM)时三种酶对同一种棉酚的反应有明显的不同,而在较高棉酚浓度(20～100μM)时棉酚对三种酶的抑制作用大体相同。对同一种酶来说,消旋棉酚,右旋棉酚和左旋棉酚对LDH的抑制作用并无差异。结论是,棉酚及其旋光异构体并不特异地抑制LDH-C_4,而在离体试验中,不能反映棉酚在体内试验中所表现的光学立体结构特异性。

Comparitive Studies on Inhibition of Lactate Dehydrogenase Isozymes by Gossypol and its Isomers

Gossypol is a potential male antifertility agent. It can inhibit sperm specific lactatedehydrogenase C4 (LDH-C4 or LDH-X) in mammals. Therefore, it has been supposedthat LDH-C4 is a target enzyme of gossypol action. The investigations of gossypolantifertility effect indicated that only (-) -gossypol revealed antifertility effect, but not(+) -gossypol. In order to understand the mechanism of gossypol antifertility effects with respect toenzymology, comparative studies on the inhibitory effect of gossypol and its isomers onLDH isozymes were carried out. Our results clearly indicated that both gossypol and its isomers had a remarkable inhi-bitory effect on these isozymes. The inhibition was temperature- and dose-dependent. Theinhibitory effect on these isozymes was much stronger at 37℃ than at 25℃. The concen-trations of gossypol required for 50% inhibition of LDH-C4 were 56μM at 37℃ and2.1μM at 25℃. Regarding the extent or response of the isozymes to gossypol and its isomers, remark-able differences between these isozymes were observed at low concentrations of gossypoland its isomers (1μM-4μM, at 37℃), but at high concentrations (20μM-100μM, 25℃), there was no significant difference observed in the extent of inhibition of gossypolon LDH-A4, LDH-C4 and LDH-B4. Our studies also indicated that in the whole range of concentrations of gossypols atthe two indicated temperatures, the extent of inhibition on each of the isozymes was al-most the same for LDH-A4, LDH-B4 and LDH-C4. No significant difference of inhibi-tion on each of the isozymes was found between gossypol and its isomers. In other words,the 3 gossypols possessed similar affinity to the same isozyme. In conclusion, gossypol and its isomers do not specifically inhibit sperm-specific lacta-te dehydrogtnase C4, which cannot be considered a target enzyme of gossypol action.Moreover, gossypol does not have stereo-specificity in its inhibitory effect on LDH-C4isozyme.