Distribution of membrane-confined phospholipases A in the rat hepatocyte.
Distribution of membrane-confined phospholipases A in the rat hepatocyte.
复制标题
膜限制磷脂酶 A 在大鼠肝细胞中的分布。
DOI：
10.1016/0005-2736(72)90189-7
复制
发表时间：
1972
期刊：
影响因子：
--
通讯作者：
P. Vignais
中科院分区：
文献类型：
--
作者：
J. Nachbaur;A. Colbeau;P. Vignais
1. A study has been made of the occurrence of phospholipases A in rat liver mitochondria, lysosomes, microsomes and plasma membrane. Some related observations on the reacylation of mitochondrial phospholipids are also presented. 2. 2. Soluble phospholipases (pH optimum 4.5) occur only in lysosomes. Membrane-bound phospholipases in mitochondria, microsomes, plasma membrane and lysosomes have an alkaline pH optimum (pH 8.5–9.0). 3. 3. The soluble lysosomal phospholipase activity is inhibited by KCl+ CaCl 2. In contrast, the membrane-bound phospholipases are all stimulated by KCl+ CaCl 2, there being an absolute requirement for Ca 2+ in the case of mitochondrial and plasma-membrane activities. 4. 4. The acid phospholipases in lysosomes show A 1 and A 2 specificity. The alkaline phospholipases in microsomes and plasma membrane have a predominant A 1 specificity while that in mitochondria is an A 2 phospholipase. 5. 5. The membrane-bound enzymes show characteristic differences in affinity for exogenous substrate. The affinity for exogenous phosphatidylethanolamine is higher in plasma membrane (K m= 40 μ M) and outer mitochondrial membrane (90 μM) than in inner mitochondrial membrane and rough endoplasmic reticulum (K m= 400 μ M). In mitochondria, endogenous phosphatidylethanolamine is hydrolyzed preferentially to added [32 P] phosphatidylethanolamine. 6. 6. The distribution of phospholipase A activity was studied in inner and outer mitochondrial membranes isolated by two different procedures. Although the distribution of phospholipase A 2 follows that of monoamine oxidase a significant activity was found in isolated inner membrane freed of matrix proteins. The mitochondrial phospholipase A 2 cannot be exclusively attributed to the outer membrane. 7. 7. The labelling, by [14 C] oleic acid, of mitochondrial membrane phosphatidylethanolamine and lecithin can be accounted for by microsomal contamination of the mitochondria. In contrast, microsomes were less active than mitochondrial outer membrane in the synthesis of phosphatidic acid from [32 P] ATP. 8. 8. Acylation of glycerophosphate produced phosphatidic acid with microsomes and lysophosphatidic acid with outer mitochondrial membrane. Accumulation of lysophosphatidic acid is attributed to a lack of acylating enzyme in the outer membrane rather than to the result of mitochondrial phospholipase action. 9. 9. These results, in agreement with some others, point to a relatively passive role of mitochondria à structure like endoplasmic reticulum in the renewal of cellular phospholipids: both as concerns an inability to attack exogenous substrate as well as a failure to re-acylate major structural components such as phosphatidylcholine and phosphatidylethanolamine. An exception to this rule may, however, be found in pathways involving minor “non-structural” components such as lysophosphatidic acid.
