A kinetic study of the oxidation by molecular oxygen of the cytochrome chain of intact yeast cells, Acetobacter suboxydans cells, and of particulate suspensions of heart muscle.
A kinetic study of the oxidation by molecular oxygen of the cytochrome chain of intact yeast cells, Acetobacter suboxydans cells, and of particulate suspensions of heart muscle.
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对完整酵母细胞、弱氧化醋杆菌细胞和心肌颗粒悬浮液的细胞色素链的分子氧氧化的动力学研究。
DOI：
10.1159/000469611
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
B. Chance
中科院分区：
文献类型：
--
作者：
G. Ludwig;S. Kuby;G. Edelman;B. Chance
本文研究了氧浓度小于6-25ms时，细胞色素c氧化酶与氧反应的稳态前动力学.对于面包酵母，在氧浓度为1.3Mumol/L时，其拟一级速度常数约为150 S-1，对应于O2与A3以约3×10(7)升当量的前进速度常数(k+1)进行的二级反应.因此，完整细胞中的膜结合的氧化酶表现出已报道的最快速的酶-底物反应之一。该值与Greenwood和Gibson在分离、溶解的细胞色素C氧化酶上的值相同。类似的k+1值由周转数[k+2(a+2)]除以为这些酵母制剂测量的Km值(公式；见正文)来计算，这表明与k+2(a+2)相比，反向反应(k-1)几乎可以忽略不计。对心肌细胞色素C氧化酶的类似计算得出k+1的值大约等于10(7)升当量-1s-1。不同的k+1值的一致性支持了酵母细胞壁不会对分子氧的运输产生显著的扩散障碍的观点。相比之下，醋酸杆菌表现出更大的Km值，并且具有不同动力学参数的末端氧化酶。
The pre-steady state kinetics of the cytochrome c oxidase reaction with oxygen were studied by a variation in the reaction time between approximately 6 and 25 ms at oxygen concentrations less than 6 mumol/l. For baker's yeast, a pseudo-first-order velocity constant of approximately 150 s-1 at 1.3 mumol/l O2 was obtained corresponding to a second-order reaction between O2 and a3 at a forward velocity constant (k+1) of approximately 3 X 10(7) liter equiv.-1s-1. Thus, the membrane-bound oxidase in the intact cell exhibits one of the most rapid enzyme-substrate reactions to be reported. The value is identical with that of Greenwood and Gibson on an isolated, solubilized cytochrome c oxidase. Similar values of k+1 are calculated from the turnover numbers [k+2 (a+2)] divided by the Km values (formula; see text) measured for these yeast preparations, which points to an almost negligible reverse reaction (k-1) compared to k+2(a+2). Similar calculations for the membrane-bound cytochrome c oxidase of heart muscle give a value of k+1 approximately equal to 10(7) liter equiv.-1s-1. The concordance of the different values of k+1 supports the view that the yeast cell wall does not impart a significant diffusion barrier to the transport of molecular oxygen. In contrast, Acetobacter suboxydans exhibits a much larger value for Km, and has a terminal oxidase of different kinetic parameters.