Dependence of peroxisomal β-oxidation on cytosolic sources of NADPH
Dependence of peroxisomal β-oxidation on cytosolic sources of NADPH
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DOI：
10.1074/jbc.274.6.3402
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发表时间：
1999-02-05
影响因子：
4.8
通讯作者：
McAlister-Henn, L
中科院分区：
文献类型：
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作者：
Minard, KI;McAlister-Henn, L
以脂肪酸为碳源的酿酒酵母的生长先前被证明需要葡萄糖-6-磷酸脱氢酶（ZWF1）或细胞质内NADP（+）特异性异柠檬酸脱氢酶（IDP2）的功能，这表明β -氧化依赖于NADPH的细胞质来源。在这项研究中，我们发现含有编码这两种酶的基因破坏的Delta IDP2 Delta ZWF1菌株在转移到含有油酸作为碳源的培养基中时表现出快速丧失活力。将缺乏异柠檬酸过氧化物酶体脱氢酶的δ IDP3菌株转移到含有二十二碳六烯酸（一种非允许碳源，需要IDP3的功能进行β -氧化）的培养基中，没有观察到这种活力丧失。这说明Delta IDP2 Delta ZWF1菌株的脂肪酸（-）表型不是简单的利用缺陷。相反，我们提出IDP2和ZWF1的共同功能是维持NADPH的显著水平，以酶促去除酵母中过氧化物酶体β氧化第一步产生的过氧化氢，而辅因子的还原形式的不足水平可能会导致死亡。这一建议得到了先前报道的Delta ZWF1突变菌株对外源过氧化氢的敏感性的支持，当使用不可发酵的碳源进行分析时，这种情况与IDP2的表达升高有关。在这些条件下，Delta ZWF1和hIDP2菌株出现了相似的缓慢生长表型，并且这两个基因的共同破坏显著加剧了H2O2表型。总的来说，这些结果表明，IDP2和ZWF1在提供抵抗内源或外源H2O2的还原等量物方面具有关键的重叠功能。
Growth of Saccharomyces cerevisiae with a fatty acid as carbon source was shown previously to require function of either glucose-6-phosphate dehydrogenase (ZWF1) or cytosolic NADP(+)-specific isocitrate dehydrogenase (IDP2), suggesting dependence of beta-oxidation on a cytosolic source of NADPH. In this study, we find that Delta IDP2 Delta ZWF1 strains containing disruptions in genes encoding both enzymes exhibit a rapid loss of viability when transferred to medium containing oleate as the carbon source. This loss of viability is not observed following transfer of a Delta IDP3 strain lacking peroxisomal isocitrate dehydrogenase to medium with docosahexaenoate, a nonpermissive carbon source that requires function of IDP3 for beta-oxidation. This suggests that the fatty acid(-) phenotype of Delta IDP2 Delta ZWF1 strains is not a simple defect in utilization. Instead, we propose that the common function shared by IDP2 and ZWF1 is maintenance of significant levels of NADPH for enzymatic removal of the hydrogen peroxide generated in the first step of peroxisomal beta-oxidation in yeast and that inadequate levels of the reduced form of the cofactor can produce lethality. This proposal is supported by the finding that the sensitivity to exogenous hydrogen peroxide previously reported for Delta ZWF1 mutant strains is less pronounced when analyses are conducted with a nonfermentable carbon source, a condition associated with elevated expression of IDP2. Under those conditions, similar slow growth phenotypes are observed for Delta ZWF1 and hIDP2 strains, and co-disruption of both genes dramatically exacerbates the H2O2s phenotype, Collectively, these results suggest that IDP2, when expressed, and ZWF1 have critical overlapping functions in provision of reducing equivalents for defense against endogenous or exogenous sources of H2O2.