PubMed Health⌕ Search

Biomedical subjects

W C McMurray

Publications and source records attributed to W C McMurray.

12 recordsLinked to original sources
PubMed1992

CDP-diacylglycerol synthesis in rat liver mitochondria.

CDP-diacylglycerol for polyglycerophosphatide biogenesis can be synthesized within rat liver mitochondria. This membrane-associated enzyme was predominantly located in the inner mitochondrial membrane. GTP had a significant effect in activating the microsomal CDP-diacylglycerol synthase, especially if the microsomes were preincubated with GTP in the presence of phosphatidic acid. This stimulatory effect of GTP on the microsomal enzyme was not detected in the mitochondrial fractions. The enzymes could be solubilized from the membrane fractions using CHAPS, and the detergent-soluble activity partially restored by addition of phospholipids. Mitochondrial and microsomal CDP-diacylglycerol synthase activity could be completely separated by anion-exchange column chromatography. The mitochondrial and microsomal CDP-diacylglycerol synthases appear to be two distinct enzymes with different localization and regulatory characteristics.

Animals↗
PubMed1990

Biosynthesis of phosphatidic acid by glycerophosphate acyltransferases in rat liver mitochondria and microsomes.

The acyltransferases that catalyze the synthesis of phosphatidic acid from labelled sn-[14C]glycero-3-phosphate and fatty acyl carnitine or coenzyme A derivatives have been shown to be present in both isolated mitochondria and microsomes from rat liver. The major reaction product was phosphatidic acid in both subcellular fractions. A small quantity of lysophosphatidic acid and neutral lipids were produced as by-products. Divalent cations had significant effects on both mitochondrial and microsomal fractions in stimulating acylation using palmitoyl CoA, but not when palmitoyl carnitine was used as the acyl donor. Palmitoyl CoA and palmitoyl carnitine could be used for acylation by both mitochondria and microsomes. Mitochondria were more permeable to palmitoyl carnitine and readily used it as the substrate for acylation. On the other hand, microsomes yielded a better rate with palmitoyl CoA and the rate of acylation from palmitoyl carnitine in microsomes was correlated with the degree of mitochondrial contamination. The enzymes were partially purified from Triton X-100 extracts of subcellular fractions. Based on the differences of substrate utilization, products formed, divalent cation effects, molecular weights, and polarity, the mitochondrial and microsomal acyltransferases appeared to be different enzymes.

Acylation↗
PubMed1978

Purification and properties of phosphatidylglycerophosphate synthetase from mammalian liver mitochondria.

The enzyme which catalyzes the synthesis of phosphatidylgly cerophosphate from an-glycerol-3-phosphated and cytidine diphosphate diacylglycerol was released from rat or pig liver mitochondrial membranes by extraction with Triton X-100 or Nonidet P-40. The detergent-extracted enzyme, like the activity of intact mitochondria, did not require added cations or lipids. The Triton extracts were fractionated by column chromatography on Bio-Gel A-1.5. The fractions obtained from the columns exhibited little activity in the standard assay system unless divalent cations were included. Additional stimulation (about twofold) was observed in the presence of added phospholipids. The cation requirement of the purified enzyme was relatively nonspecific with Mg2+, Ba2+, or Ca2+ providing maximal activity in the 10mM range. Either Mn2+ or Co2+ were stimulatory at somewhat lower concentrations but higher concentrations were inhibitory. Other cations such as Cd2+, Zn2+,Hg2+, or Cu2+ were ineffective as cofactors, and in the presence of Mg2+ inhibited the reaction at concentrations greater than 0.5 mM. The phospholipik stimulation was obtained specifically with phosphatidylethanolamines from natural or synthetic sources. Other diacylglycerophosphatides or lysophosphatides including lysophosphatidylethanolamine were ineffective.

Animals↗
PubMed1978

Release of cryptic monoamine oxidase activity by growth of BHK-21 cells in D-chloramphenicol.

The activity of monoamine oxidase, a marker enzyme of the outer mitochondrial membrane, is stimulated in BHK cells grown in the presence of 100 microgram ml-1 D-chloramphenicol. The observed stimulation can be reversed by removal of the antibiotic. Addition of the non-ionic detergent Triton X-100, to cell homogenates results in an elevation of the enzyme activity similar to that produced by D-chloramphenicol treatment. The activation by chloramphenicol is apparently related to a release of cryptic monoamine oxidase activity.

Cells, Cultured↗
PubMed1977

Mitochondrial biogenesis in cultured animal cells. I. Effect of chloramphenicol on morphology and mitochondrial respiratory enzymes.

The effects of chloramphenicol on the morphology and respiratory enzymes of BHK-21 cells in spinner culture have been examined with time. Cells treated with chloramphenicol double twice before growth ceases; these cells have increased size as measured by several techniques. Mitochondria are enlarged and appear to degenerate with prolonged treatment. Cytochrome c oxidase and succinate cytochrome c reductase activities are reduced while there is no decrease in the activities of monoamine oxidase, glutamate dehydrogenase or NADPH-cytochrome c reductase. Cytochromes aa3 and b disappear on treatment while cytochromes c + c1 appears to be unaffected. All these effects are reversible if chloramphenicol is removed within a limited period of time.

Cell Division↗
PubMed1977

Mitochondrial biogenesis in cultured mammalian cells. II. Mitochondrial protein and phospholipid synthesis in chloramphenicol-treated BHK-21 cells.

The effect of growth of BHK-21 cells in chloramphenicol on the synthesis of cellular proteins and phospholipids has been examined. The incorporation of leucine into total cellular proteins, or into the proteins of specific subcellular fractions are not significantly reduced by cell culture in the presence of chloramphenicol. In cells treated with cycloheximide, a small amount of chloramphenicol-sensitive labelling of protein was detected within the first hour of exposure to the drug. Chloramphenicol inhibits the incorporation of delta-amino-levulinic acid into hemoproteins, only if it is present during both the 48-h culturing and 4-h labelling period. De novo synthesis of cellular lipids as measured by pulse labelling with 32Pi or [3H]glycerol, is decreased in chloramphenicol-treated cells. This decrease is observed in all sub-cellular fractions, although the mitochondrial fraction is most affected. All phospholipids are affected, with diphosphatidylglycerol labelling reduced to the greatest extent. Although fatty acid synthesis is inhibited, the labelling of diphosphatidylglycerol with fatty acids is stimulated on chloramphenicol treatment.

Acetates↗
PubMed1977

Mitochondrial biogenesis in cultured mammalian cells. III. Synthesis of mitochondrial phospholipids by subcellular fractions isolated from normal and chloramphenicol-treated BHK-21 cells.

The capacity of subcellular fractions isolated from chloramphenicol-treated BHK-21 cells to synthesize various mitochondrial phospholipids in vitro and examined. Both mitochondria and microsomes showed the capacity to acylate sn-glycerol 3-phosphate and dihydroxyacetone phosphate to lysophosphatidic acid and acyldihydroxyacetone phosphate and subsequently to phosphatidic acid. Both processes are inhibited in mitochondria from chloramphenicol-treated cells. The synthesis of CDPdiacylglycerol in mitochondria or microsomes, and the synthesis of phosphatidylinositol and of phosphatidylcholine in microsomes were stimulated in treated cells. A slight stimulation was also observed in the synthesis of phosphatidylglycerol and diphosphatidylglycerol when the labelled precursor was sn-glycerol 3-phosphate in treated cells, although the process was inhibited with labelled glycerol as the precursor. Conversion of phosphatidylglycerol phosphate to phosphatidylglycerol by mitochondria was rate limiting unless the post-microsomal supernatant fraction was added. These results are discussed in regard to the observed inhibition of phospholipid synthesis in BHK-21 cells in culture by chloramphenicol.

Cell Line↗
PubMed1976

Intracellular phospholipid transfer and exchange.

The intracellular transfer of phospholipids in rat liver was studied. The factors affecting the transport and the role of phospholipid transfer proteins in this process were investigated. The procedure was based upon the labelling of microsomal phospholipids with either 14C or 32P, and incubation with unlabelled mitochondria in an in vitro system. The re-isolated mitochondria became labelled demonstrating an exchange of phospholipid between the two membranes. The transfer was stimulated by the addition of high-speed supernatant, was unaffected by the addition of ATP, but did not occur at 0 degrees C. Phospholipid transfer between liposomes and mitochondria was shown to occur, suggesting that the participation of natural membranes is not required for transfer to take place. The conditions required were found to be similar, and the high speed supernatant promoted transfer to the same extent as when labelled microsomes acted as the donor. The transfer activity of the high-speed supernatant was abolished by treatment with sulphydryl-blocking agents. Beef supernatant was adjusted to pH 5.1 and the activity remained in the supernatant. The pH 5.1 supernatant was applied to a Sephadex G-75 column and two active fractions were collected. The higher molecular weight fraction contained several proteins and stimulated the transfer of phosphatidylcholine and phosphatidylethanolamine. The lower molecular weight active fraction contained a protein which specifically stimulated the transfer of phosphatidylcholine.

Animals↗
PubMed1975

Biosynthesis of mitochondrial phospholipids using endogenously generated diglycerides.

When isolated mitochondria or microsomes from rat liver were treated with phospholipase C, the incorporation of radioactive phospholipid precursors was markedly enhanced, presumably as a result of production of diglycerides by hydrolysis of endogenous phospholipids. Incorporation of CDP[14C]choline into lecithin in rat liver or BHK-21 mitochondria could be attributed to residual contamination from elements of the endoplasmic reticulum, with added diglycerides or with endogenous diglycerides produced by the phospholipase C treatment. A similar stimulation of [gamma32P]ATP incorporation into phospholipids was observed with exogenous or endogenous diglycerides, but the mitochondrial diglyceride kinase in either case was also related to the degree of microsomal contaminants. It was concluded that previous studies showing negligible capacity of mitochondria for lecithin biosynthesis de novo were not explainable on the basis of limited accessibility of added diglycerides, and that formation of phosphatidic acid by diglyceride kinase was not of significance in rat liver mitochondria.

Adenosine Triphosphate↗