Greenberg M L, Hubbell S, Lam C
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor 48109-0606.
Mol Cell Biol. 1988 Nov;8(11):4773-9. doi: 10.1128/mcb.8.11.4773-4779.1988.
The enzyme phosphatidylglycerolphosphate synthase (PGPS; CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase; EC 2.7.8.5) catalyzes the committed step in the synthesis of cardiolipin, a phospholipid found predominantly in the mitochondrial inner membrane. To determine whether PGPS is regulated by cross-pathway control, we analyzed PGPS expression under conditions in which the regulation of general phospholipid synthesis could be examined. The addition of inositol resulted in a three- to fivefold reduction in PGPS expression in wild-type cells in the presence or absence of exogenous choline. The reduction in enzyme activity in response to inositol was seen in minutes, suggesting that inactivation or degradation of the enzyme plays an important role in inositol-mediated repression of PGPS. In cho2 and opi3 mutants, which are blocked in phosphatidylcholine synthesis, inositol-mediated repression of PGPS did not occur unless choline was added to the media. Three previously identified genes that regulate general phospholipid synthesis, INO2, INO4, and OP11, did not affect PGPS expression. Thus, ino2 and ino4 mutants, which are unable to derepress biosynthetic enzymes involved in general phospholipid synthesis, expressed wild-type levels of PGPS activity under derepressing conditions. PGPS expression in the opi1 mutant, which exhibits constitutive synthesis of general phospholipid biosynthetic enzymes, was fully repressed in the presence of inositol and partially repressed even in the absence of inositol. These results demonstrate for the first time that an enzymatic step in cardiolipin synthesis is coordinately controlled with general phospholipid synthesis but that this control is not mediated by the same genetic regulatory circuit.
磷脂酰甘油磷酸合酶（PGPS；CDP二酰甘油-甘油-3-磷酸3-磷脂酰转移酶；EC 2.7.8.5）催化心磷脂合成中的关键步骤，心磷脂是一种主要存在于线粒体内膜的磷脂。为了确定PGPS是否受交叉途径控制调节，我们在可以检测一般磷脂合成调节的条件下分析了PGPS的表达。无论有无外源性胆碱，添加肌醇都会使野生型细胞中PGPS的表达降低三到五倍。几分钟内就观察到了酶活性因肌醇而降低，这表明酶的失活或降解在肌醇介导的PGPS抑制中起重要作用。在磷脂酰胆碱合成受阻的cho2和opi3突变体中，除非向培养基中添加胆碱，否则不会发生肌醇介导的PGPS抑制。三个先前鉴定的调节一般磷脂合成的基因INO2、INO4和OP11不影响PGPS的表达。因此，无法解除对参与一般磷脂合成的生物合成酶抑制的ino2和ino4突变体，在解除抑制条件下表达野生型水平的PGPS活性。opi1突变体表现出一般磷脂生物合成酶的组成型合成，其PGPS表达在有肌醇存在时被完全抑制，甚至在没有肌醇时也被部分抑制。这些结果首次证明，心磷脂合成中的一个酶促步骤与一般磷脂合成协同控制，但这种控制不是由相同的遗传调节回路介导的。
