ISOFORMS OF YEAST CYTOCHROME-C-OXIDASE SUBUNIT-V AFFECT THE BINUCLEAR REACTION-CENTER AND AFTER THE KINETICS OF INTERACTION WITH THE ISOFORMS OF YEAST CYTOCHROME-C
ISOFORMS OF YEAST CYTOCHROME-C-OXIDASE SUBUNIT-V AFFECT THE BINUCLEAR REACTION-CENTER AND AFTER THE KINETICS OF INTERACTION WITH THE ISOFORMS OF YEAST CYTOCHROME-C
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DOI：
10.1074/jbc.270.1.110
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发表时间：
1995-01-06
影响因子：
4.8
通讯作者：
POYTON, RO
中科院分区：
文献类型：
--
作者：
ALLEN, LA;ZHAO, XJ;POYTON, RO
V亚基是酵母细胞色素C氧化酶的核编码亚基之一，有Va和Vb两种亚型。这些改变了体内全酶分子内电子转移的速率(Watland，R.A.，Basu，A.，Chance，B.和Poyton，R.O.(1991)J.Biol)。陈。266、4180-4186)。Vb的同工酶比Va的同工酶具有更高的周转率和分子内转移速率。为了确定这些异构体如何影响催化作用，我们研究了它们对双核反应中心的影响，以及对细胞色素c氧化酶与酵母细胞色素c的两种异构体iso-1和iso-2相互作用的影响。一氧化碳与血红素a(3)连接的红外光谱显示，在与Vb的同工酶中，双核反应中心为单一构象，而在与Va的同工酶中，为两个离散构象。所有四种同工酶与各亚基V亚型和两种细胞色素c亚型相互作用的动力学是两相的，有高亲和力和低亲和力的电子转移反应。一般来说，细胞色素c和亚基V的异构体不会改变K-m，但会影响Tnmax。每种细胞色素c亚型的高亲和力和低亲和力部位的Tnmax均较高。ISO-1-细胞色素c支持比ISO-2-细胞色素c更高的Tnmax。令人惊讶的是，这两组异构体对Tnmax的组合效应因细胞内共表达的一对异构体(iso-1-细胞色素c和亚基Va或iso-2和亚基Vb)而最小化。综上所述，这些发现支持V亚基异构体调节催化的结论，并表明它们通过影响双核反应中心的环境或结构来调节催化。他们还认为，两种细胞色素c亚型和两种亚基V亚型的共同表达有助于最小化亚基V亚型带来的电子转移速率的差异。
Subunit V, one of the nuclear coded subunits of yeast cytochrome c oxidase, has two isoforms, Va and Vb. These alter the in vivo intramolecular rates of electron transfer within the holoenzyme (Waterland, R. A., Basu, A., Chance, B., and Poyton, R. O. (1991) J. Biol. Chen. 266, 4180-4186). The isozyme with Vb has a higher turnover rate and a higher intramolecular transfer rate than the isozyme with Va. To determine how these isoforms affect catalysis, we have examined their effects on the binuclear reaction center and on the interaction between cytochrome c oxidase and the two isoforms, iso-1 and iso-2, of yeast cytochrome c. Infrared spectroscopy of carbon monoxide liganded to heme a(3) has revealed a single conformer for the binuclear reaction center in the isozyme with Vb but two discrete conformers in the isozyme with Va. The kinetics of interaction for all four pairwise combinations of isozymes with each subunit V isoform and the two cytochrome c isoforms are biphasic, with high and low affinity electron transfer reactions. In general, the isoforms of cytochrome c and subunit V do not alter the K-m but do affect the TNmax. The TNmax for isozymes carrying Vb are higher at both high and low affinity sites for each cytochrome c isoform. Iso-1-cytochrome c supports a higher TNmax than Iso-2-cytochrome c. Surprisingly, the combinatorial effect of both sets of isoforms on TNmax is minimized with the pairs of isoforms (iso-1-cytochrome c and subunit Va or iso-2 and subunit Vb) that are co-expressed in cells. Together, these findings support the conclusion that the subunit V isoforms modulate catalysis and suggest that they do so by affecting the environment or structure of the binuclear reaction center. They also suggest that the coexpression of the two cytochrome c isoforms with two subunit V isoforms serves to minimize differences in electron transfer rates brought about by the subunit V isoforms.