OXIDATION-REDUCTION POTENTIALS OF TURKEY LIVER XANTHINE DEHYDROGENASE AND ORIGINS OF OXIDASE AND DEHYDROGENASE BEHAVIOR IN MOLYBDENUM-CONTAINING HYDROXYLASES
OXIDATION-REDUCTION POTENTIALS OF TURKEY LIVER XANTHINE DEHYDROGENASE AND ORIGINS OF OXIDASE AND DEHYDROGENASE BEHAVIOR IN MOLYBDENUM-CONTAINING HYDROXYLASES
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DOI：
10.1042/bj1630279
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发表时间：
1977-01-01
影响因子：
4.1
通讯作者：
COUGHLAN, MP
中科院分区：
文献类型：
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作者：
BARBER, MJ;BRAY, RC;COUGHLAN, MP
氧化还原电位的各种中心的酶黄嘌呤脱氢酶（EC www.example.com）从火鸡肝测定电位滴定介质染料的存在下，与低温EPR光谱。值为25 °。在pH8.2的焦磷酸盐缓冲液中，Mo（VI）/Mo（V）（快速），-350 ±-。20 mV; Mo（V）（快速）/Mo（IV），-362 ±。20 mV; Fe-S Iox./ Fe-S Ired.，-295。15 mV; Fe-S IIox./ Fe-S IIred.，-292。15 mV; FAD/FADH;-359. ±. 20 mV; FADH. cntdot./ FADH 2，-366.+-。20 mV。FADH.cntdot./的此值FADH 2电位比牛奶黄嘌呤氧化酶的相应电位低130 mV，这是两种酶之间差异的原因。当考虑到酶的某些干扰时，用黄嘌呤滴定时酶行为的差异可由电位来解释。讨论了由尿酸结合引起的酶的Mo电位的增加。尽管尿酸/黄嘌呤的电位（-440 mV）有利于脱氢酶的完全还原，但在周转期间，由于动力学原因，仅FADH。由于预期只有FADH 2与O2反应，因此解释了脱氢酶缺乏氧化酶活性。以NAD+为电子受体的2种酶的反应性与电位的关系进行了讨论。
Redox potentials for the various centers in the enzyme xanthine dehydrogenase (EC 1.2.1.37) from turkey liver were determined by potentiometric titration in the presence of mediator dyes, with low-temperature EPR spectroscopy. Values at 25.degree. C in pyrophosphate buffer, pH 8.2, are: Mo(VI)/Mo(V) (rapid), -350 .+-. 20 mV; Mo(V) (rapid)/Mo(IV), -362 .+-. 20 mV; Fe-S Iox./Fe-S Ired., -295 .+-. 15 mV; Fe-S IIox./Fe-S IIred., -292 .+-. 15 mV; FAD/FADH; -359 .+-. 20 mV; FADH.cntdot./FADH2, -366 .+-. 20 mV. This value of the FADH.cntdot./FADH2 potential, which is 130 mV lower than the corresponding one for milk xanthine oxidase, accounts for many of the differences between the 2 enzymes. When allowance is made for some interference by desulfo enzyme, then differences in the enzymes'' behavior in titration with xanthine are accounted for by the potentials. Increases in the Mo potentials of the enzymes caused by the binding of uric acid are discussed. Though the potential of uric acid/xanthine (-440 mV) is favorable for full reduction of the dehydrogenase, during turnover, for kinetic reasons, only FADH.cntdot. and very little FADH2 is produced from it. Since only FADH2 is expected to react with O2, lack of oxidase activity by the dehydrogenase is explained. Reactivity of the 2 enzymes with NAD+ as electron acceptor is discussed in relation to the potentials.