Evidence for the Biosynthetic Difference between Isolated Mitochondria and Microsomes from Guinea-Pig and Rat Liver Regarding Lysophospharidic Acid, Phosphatidic Acid, CDP-Diglyceride, Phosphatidylglycerol, and Cardiolipin

Abstract

The enzymatic activities of marker enzymes (NADPH – cytochrome c reductase and glucose-6-phosphatase) and synthetic enzymes (acyl-CoA:sn-glycero-3-phosphate acyltransferase, CTP:sn-3-phosphatidic acid cytidyltransferase, and CDP-diglyceride:sn-glycero-3-phosphate phosphatidyltransferase) were measured in both isolated mitochondria and microsomes from liver of guinea pig and rat. Results thus obtained show a significant difference in activities of these enzymes between subcellular particles within species and between two examined species. The activity of acyl-CoA:glycero-3-phosphate acyltransferase in guinea-pig mitochondria parallels the activity of microsomal marker enzymes in this fraction, while in rat liver mitochondria the activity is relatively higher and cannot be accounted for by the microsomal content as determined by marker enzymes. Implications of these results regarding mitochondrial autonomy in the biosynthesis of polyglycero-phosphatides and their precursors are discussed.

Biosynthesis of phosphatidylglycerol and phosphatidylglycerolphosphate in submitoehondrial membranes isolated from guinea pig liver is absolutely dependent on CDP-diglycerides imported from microsomal membranes

“…Whether this variation results from species' differences or from different experimental conditions (no absolute dependence on CBPdig was established by Hostetler and Van Den Bosch 1972) remains to be determined. With respect to the differences between species, we demonstrated that the acylation of sn-glycero-3-phosphate to yield lyso-PtdA and PtdA in mitochondria isolated from guinea pig liver can be attributed to microsomal contamination, while in mitochondria isolated from rat liver the same acylation appears to be an intrinsic property of the mitochondrial membrane (Davidson and Stanacev 1974). Finally, this study has established that the biosynthesis of PtdGP and PtdG in submitochondrial membranes absolutely depends on CDP-dig.…”

“…Our previous studies showed that the mitochondrial biosynthesis of CBP-dig can be attributed to microsomal contamination (Davidson andStanacev 1972, 1974) and that the transfer of CDP-dig from microsomal to mitochondrial membranes, isolated from guinea pig liver, can take place (Stuhne-Sekalec et 01. 1986).…”

“…and CDP-dig in guinea pig liver can be attributed to microsomal contamination (Davidson and Stanacev 1972). We have also established that microsomal CDP-dig containing either spin-labelled (5-, 12-, and 16-nitroxide fatty acids) or natural fatty acids can be transferred to mitochondria and can participate in the mitochondrial CDP-diglyceridedependent biosynthesis of polyglycerophosphatides (PtdGP, PtdG, and diphosphatidylglycerol or cardiolipin) (reactions 3 and 4) (Stuhne-Sekalec et al.…”

“…Assays for acyl-CoA:sn-glycerol-3-phosphate acyltransferase, CTP:sn-3-phosphatidate cytidyltransferase, and CDP-diglyceride: sn-glycerol-3-phosphate phosphatidyltransferasc were described in detail in our previous communications (Stuhne-Sekalec et al 1986;Davidson and Stanacev 1972;Stuhne-Sekalec and Stanacev 1987).…”

Distribution ofcis-Vaccenic Acid in Chinese Hamster V79-R Cells

“…The low fatty acyd desaturase activity in the mitochondrial fraction may be due to contamination by microsomes. Hence, it seems likely that the higher specificity of CL synthesizing enzyme system to the molecular species containing 16:1 (Lt9) and 18:1 (Ltll) may be a cause for high contents of 16: 1 (Lt9) and 18: 1 (Ltll) in CL.…”