【摘要】 以果糖-1,6-二磷酸(FDP)为底物,正常小鼠肝匀浆无克奈特瑞效应;但以磷酸烯醇式丙酮酸(PEP)为底物,则在正常小鼠肝中也出现此效应;而小鼠Hep A 腹水肝癌(简称Hep A)细胞匀浆中由这两种底物所引起的此效应均十分明显。Hep A中,丙酮酸激酶(PyK)的活性为正常小鼠肝的4.7倍。在研究PyK 和克奈特瑞效应关系时发现:1.PyK 的底物PEP 可抑制线粒体中琥珀酸、丙酮酸和NADH 的氧化,而琥珀酸和NADH 又可抑制PEP 的酵解;2.加入从Hep A中纯化的K 型PyK,可抑制琥珀酸的氧化,加强PEP 对琥珀酸氧化的抑制,且其对FDP 氧化的抑制率和K 型PyK 的加入量成正相关;3.用L-苯丙氨酸抑制PyK 后,可减小PEP 对琥珀酸氧化的抑制,并使PEP 的酵解降低;4.加入氧化磷酸化的解联剂2,4-二硝基酚(DNP),可使PEP 的酵解随DNP 浓度的增加而增加;(5)加入正常小鼠肝的线粒体,可使正常小鼠肝匀浆的呼吸增高,酵解降低;并使Hep A 的克奈特瑞效应逆转。此外,加入外源性的ADP 既可促进呼吸,又可促进酵解;加入可消耗ADP 的磷酸肌酸和肌酸激酶,则使呼吸和酵解均降低。K 型PyK 加强PEP 对琥珀酸氧化的抑制效率也和ADP 的浓度密切相关。这些实验结果都证明:胞液中的PyK 和线粒体之间存在着对ADP 的竞争。并且胞液中增高的PyK 对ADP 的有效的夺取,很可能是导致癌瘤中克奈特瑞效应的一个重要机理。更多还原

【Abstract】 In Hep A ascites hepatoma (Hep A),addition of fructose-1,6-diphosphate (FDP)or phosphoenol pyruvate (PEP) brought about a marked Crabtree effect,but innormal mouse liver,this effect was seen only when PEP was used as substrate,andthe values of the Crabtree effect were much less than that in Hep A.The pyruvatekinase (PyK) activity in Hep A was 4.7 times as high as that in normal mouse liver.During studies on the relationship between PyK and the Crabtree effect,the followingfacts were revealed:(1) The oxidation of succinate,pyruvate and NADH was inhlbited by the substrate of PyK,PEP,while glycolysis of PEP was inhibited bysuccinate and NADH.(2) The oxidation of succinate was inhibited by the addition ofpurified type K PyK from Hep A,and the inhibitory effect of PEP on succinateoxidation was also enhanced by type K PyK.Moreover,the inhibitory rate of FDPoxidation by type K PyK was increased progressively with increasing amounts oftype K PyK added.(3) When PyK was inhibited by L-phenylalanine,the inhibitionof succinate oxidation by PEP was reduced,and the glycolysis of PEP was alsoredusod simultaneously.(4) With 2,4-dinitrophenol (DNP) as an uncoupling agentof oxidative phosphorylation,glycolysis of PEP was increased with increase in theconcentration of DNP added.(5) When isolated mitochondria from normal mousecliver were added,the respiration in normal mouse liver homogenate was increased,the glycolysis decreased,and the Crabtree effect in Hep A was reversed.In additionexogenous ADP stimulated both respiration and glycolysis,and an ADP consumptionsystem,creatine kinase and creatine phosphate,inhibited both processes,and theinhibition of type K PyK plus PEP on succinate oxidation varied with the ADPconcentrations in the reaction mixture.All the above mentioned results have proventhat competition for ADP exists between cytosol PyK and mitochondria,and theromarkable increase in PyK activity in malignant tumors must effectively enhancethe ability of its cytosol to compete for ADP with mitochondria.This might be theessential mechanism of the Crabtree effect.更多还原