Lee A C, Xu X, Blachly-Dyson E, Forte M, Colombini M
Department of Zoology, University of Maryland, College Park 20742, USA.
J Membr Biol. 1998 Jan 15;161(2):173-81. doi: 10.1007/s002329900324.
In addition to the POR1 gene, which encodes the well-characterized voltage dependent anion-selective channel (YVDAC1) of the mitochondrial outer membrane, the yeast Saccharomyces cerevisiae contains a second gene (POR2) encoding a protein (YVDAC2) with 50% sequence identity to YVDAC1. Mitochondria isolated from yeast cells deleted for the POR1 gene (delta por1) had a profoundly reduced outer membrane permeability as measured by the ability of an intermembrane space dehydrogenase to oxidize exogenously added NADH. Mitochondria missing either YVDAC1 or both YVDAC1 and YVDAC2 showed a 2-fold increase in the rate of NADH oxidation when the outer membrane was deliberately damaged. Mitochondria from parental cells showed only a 10% increase indicating that the outer membrane is highly permeable to NADH. In the absence of YVDAC1, we calculate that the outer membrane permeability to NADH is reduced 20-fold. The low NADH permeability in the presence of YVDAC2 was not due to the low levels of YVDAC2 expression as mitochondria from cells expressing levels of YVDAC2 comparable to those of YVDAC1 in parental cells showed no substantial increase in NADH permeability, indicating a minimal role of YVDAC2 in this permeability. The residual permeability may be due to other pathways because cells missing both genes can still grow on nonfermentable carbon sources. However, YVDAC1 is clearly the major pathway for NADH flux through the outer membrane in these mitochondria.
除了编码线粒体外膜中特征明确的电压依赖性阴离子选择性通道（YVDAC1）的POR1基因外，酿酒酵母还含有第二个基因（POR2），该基因编码一种与YVDAC1具有50%序列同一性的蛋白质（YVDAC2）。通过膜间隙脱氢酶氧化外源添加的NADH的能力来测量，从缺失POR1基因的酵母细胞（delta por1）中分离出的线粒体，其外膜通透性显著降低。当外膜受到人为损伤时，缺失YVDAC1或同时缺失YVDAC1和YVDAC2的线粒体，其NADH氧化速率增加了2倍。来自亲代细胞的线粒体仅增加了10%，这表明外膜对NADH具有高度通透性。在没有YVDAC1的情况下，我们计算出外膜对NADH的通透性降低了20倍。在存在YVDAC2的情况下，NADH通透性较低并不是由于YVDAC2表达水平低，因为来自表达与亲代细胞中YVDAC1相当水平的YVDAC2的细胞的线粒体，其NADH通透性没有显著增加，这表明YVDAC2在这种通透性中起最小作用。剩余的通透性可能归因于其他途径，因为同时缺失这两个基因的细胞仍然可以在非发酵碳源上生长。然而，YVDAC1显然是这些线粒体中NADH通过外膜的主要途径。
