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S D Clarke

Publications and source records attributed to S D Clarke.

At least 91 records · Page 5Linked to original sources
PubMed1986

Partial Purification and Characterization of the Quinol Oxidase Activity of Arum maculatum Mitochondria.

The menadiol oxidase activity of Arum maculatum mitochondria has been solubilized and fractionated. A preparation has been obtained which has an increased specific activity and a greatly decreased polypeptide composition when compared to the mitochondria. This preparation retains normal inhibitor sensitivities in that the oxidation of menadiol remains insensitive to cyanide and is inhibited by aromatic hydroxamates. Metal analyses of the preparation showed that only iron was closely correlated with the oxidase activity. No unusual lipid components were detected in the preparation. The results are discussed in relation to chemical quinol oxidation mechanisms and to several recent hypotheses concerning the nature of the higher plant alternative oxidase.

Journal Article↗
PubMed1985

Role of sterol carrier protein in cholesterol metabolism.

This report summarizes our recent studies on the protein known as sterol carrier protein (SCP) or fatty acid binding protein (FABP). SCP is a highly abundant, ubiquitous protein with multifunctional roles in the regulation of lipid metabolism and transport. SCP in vitro activates membrane-bound enzymes catalyzing cholesterol synthesis and metabolism, as well as those catalyzing long chain fatty acid metabolism. SCP also binds cholesterol and fatty acids with high affinity and rapidly penetrates cholesterol containing model membranes. Studies in vivo showed SCP undergoes a remarkable diurnal cycle in level and synthesis, induced by hormones and regulated in liver by translational events. SCP rapidly responds in vivo to physiological events and manipulations affecting lipid metabolism by changes in level. Thus SCP appears to be an important regulator of lipid metabolism. Preliminary evidence is presented that SCP is secreted by liver and intestine into blood and then taken up by tissues requiring SCP but incapable of adequate SCP synthesis.

Animals↗
PubMed1985

Fatty acid-mediated disaggregation of acetyl-CoA carboxylase in isolated liver cells.

In recent years the rapid regulation of acetyl-CoA (AcCoA) carboxylase (EC 6.4.1.2) has become of major interest because of the important role of malonyl-CoA in fatty acid synthesis, ketogenesis, and triglyceride production. AcCoA carboxylase is acutely regulated by two mechanisms: 1) phosphorylation-dephosphorylation and 2) polymer-protomer transition. Until recently polymer-protomer transition of AcCoA carboxylase in vivo has escaped detection. We developed a technique that estimates the intracellular proportion of polymer and protomer forms of AcCoA carboxylase based on the differential sensitivity of polymeric and protomeric AcCoA carboxylase to avidin inactivation. When the enzyme is in its highly aggregated conformation, the biotin prosthetic group of AcCoA carboxylase is protected from avidin binding. Thus the polymeric AcCoA carboxylase is more resistant than the protomeric conformation to avidin inactivation. Utilizing this technique with isolated liver cells we have been able to develop a model for the involvement of free fatty acids and glucagon in regulating polymer-protomer transition of AcCoA carboxylase, and the role of polymer as an intracellular determinant of AcCoA carboxylase activity. Our data suggest that the physiological regulation of AcCoA carboxylase involves the interaction of the phosphorylation mechanism with fatty acid-induced depolymerization. We propose that during periods of food deprivation the elevation in fatty acid-CoA esters promotes depolymerization of AcCoA carboxylase. In addition, glucagon induces phosphorylation of AcCoA carboxylase, which inhibits the enzyme's activity and facilitates acyl-CoA binding and depolymerization. The two separate mechanisms for regulating hepatic AcCoA carboxylase may work in concert to modulate the level of the regulatory metabolite malonyl-CoA.

Acetyl-CoA Carboxylase↗
PubMed1984

Resistance of lung fatty acid synthesis to inhibition by dietary fat in the meal-fed rat.

One-half of the palmitate utilized by the lung for production of the surfactant phospholipid, dipalmitoyl phosphatidylcholine, originates from de novo palmitate synthesis in the lung. In this report the lung was examined for the influence of dietary fat on the lung de novo fatty acid synthesis pathway. Lung lipogenesis was reduced by fasting and accelerated by carbohydrate refeeding or insulin injection. However, in general lung fatty acid synthesis was unaffected by dietary fat. Supplementing one meal (high glucose diet) with as much as 36% additional fat kilocalories did not suppress lung fatty acid synthesis. An inhibition of fatty acid synthesis resulted from a fat supplement of +60 and +120% of meal kilocalories, but this inhibition was likely due to an attenuated rate of glucose absorption. Ingestion of a high carbohydrate diet supplemented with 10, 17, or 30% added kilocalories as safflower oil or palmitate had no effect on lipogenesis after 10 days. On the other hand, liver fatty acid synthesis and acetyl-CoA carboxylase were selectively suppressed by safflower oil, whereas dietary palmitate was ineffective as an inhibitor of lipogenesis. These data clearly demonstrate that the well-characterized preferential suppression of liver lipogenesis by dietary polyunsaturated fats does not extend to lung tissue, and, more importantly, the inhibition of liver lipogenesis is not secondary to an essential fatty acid deficiency. The marked resistance of lung fatty acid synthesis to inhibition by dietary fat might be a biological protective mechanism to ensure adequate palmitate for dipalmitoyl phosphatidylcholine synthesis.

Acetyl-CoA Carboxylase↗
PubMed1983

Rapid changes in chick liver acetyl-CoA carboxylase indicative of phosphorylation control.

Liver fatty acid synthesis was suppressed 75,95 and 90% within 1, 2 and 4 hrs respectively of depriving chicks of food. Accompanying this rapid drop in lipogenesis was a marked reduction in acetyl-CoA carboxylase activity, i.e., 40 and 75% decrease after 2 and 4 hrs of fasting. Adding 10 mM citrate to the crude liver supernatant, or incubating the supernatant at 37 degrees, 30 min increased activity of the briefly fasted birds, but neither method restored carboxylase activity to fed level. Heat and citrate activation were additive and together resulted in an activity comparable to the fed condition. The heat-dependent activation was accelerated by exogenous phosphoprotein phosphatase, and completely blocked by 100 mM NaF. Thus, enhancement of carboxylase activity from liver of briefly fasted chicks appears to be a dephosphorylation process. This is the first report indicating acute changes in chick carboxylase activity may involve a phosphorylation-dephosphorylation mechanism.

Acetyl-CoA Carboxylase↗
PubMed1982

Reconstitution of cytochrome bc1 complex into lipid vesicles and the restoration of uncoupler sensitivity.

Beef heart mitochondrial bc1 complex (ubiquinone--cytochrome c oxidoreductase) has been assayed by its ability to catalyse the reaction of duroquinol reduction of ferricytochrome c. When the isolated complex is reincorporated into lipid vesicles, the enzyme-catalysed electron transfer rate becomes uncoupler-sensitive. Initial experiments suggest that a protonmotive force is generated across the vesicles when electron transfer is initiated. Both delta psi and delta pH components of this protonmotive force then influence an internal rate constant of the bc1 complex.

Animals↗
PubMed1982

Suppression of rat liver fatty acid synthesis by eicosa-5,8,11,14-tetraynoic acid without a reduction in lipogenic enzymes.

In meal-fed rats supplementation of safflower oil (5 g per 100 g diet) to a fat-free basal diet resulted in the characteristic suppression of liver fatty acid synthetase and acetyl-CoA carboxylase activities, which was accompanied by a 60% decrease in the rate of hepatic fatty acid synthesis. The decline in activity of these lipogenic enzymes was completely prevented by adding 0.05% eicosa-5,8,11,14-tetraynoic acid (TYA) to the safflower oil diet. Fatty acid analysis of the livers indicated that TYA significantly impaired the conversion of linoleate to arachidonate. Apparently the selective suppression of lipogenic enzymes by dietary linoleate is not caused by linoleate per se but requires its conversion to longer-chain fatty acids and/or protaglandins. In spite of high activities of fatty acid synthetase and acetyl-CoA carboxylase, liver fatty acid synthesis continued to be inhibited by the safflower oil + TYA dietary regimen. This continued inhibition of lipogenesis was due to the TYA, because addition of TYA to the fat-free diet precipitated a significant decline in liver fatty acid synthesis without a drop in lipogenic enzymes. Inhibition of fatty acid synthesis by TYA could not be attributed to a decrease in liver glucose utilization based on hepatic glycogen concentration, nor was it due to a reduction in the fraction of catalytically active polymeric acetyl-CoA carboxylase based on sensitivity of the enzyme activity to avidin.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1981

Suppression of hepatocyte fatty acid synthesis by albumin-bound linoleate involves depolymerization of acetyl-CoA carboxylase filaments.

Digitonin treatment of chick liver cells in monolayer culture results in plasma membrane perforations due to digitonin removal of membrane cholesterol. The amount and rate of acetyl-CoA carboxylase activity that escapes from the hepatocyte during digitonin treatment is positively related to the amount of protomeric carboxylase in the cells. Incubation of chick liver cells in culture with albumin-bound linoleate (60 min) caused a 3-fold increase in the amount of carboxylase activity released during exposure of cells to digitonin. Concomitant with the enhanced release of carboxylase activity was an 85% reduction in fatty acid synthesis induced by linoleate. Apparently, acute suppression of hepatocyte fatty acid synthesis by media free fatty acids resulted, in part, from a change in carboxylase conformation from the active polymeric state to the inactive protomeric form.

Acetyl-CoA Carboxylase↗
PubMed1981

Coordinate suppression of liver acetyl-CoA carboxylase and fatty acid synthetase by polyunsaturated fat.

Polyunsaturated fats (PUFA) suppressed hepatic fatty acid synthesis and the activities of lipogenic enzymes more effectively than did saturated fats. The activity of glycolytic enzymes--glucokinase, phosphofructokinase and pyruvate kinase--were not affected by PUFA. The absolute rate of liver fatty acid synthesis after meal ingestion was very similar to the maximal activities of acetyl-CoA carboxylase and fatty acid synthetase. When PUFA was supplemented to a fat-free diet, the activities of carboxylase and synthetase decreased similarly over 3 days. During the 3 days, the concentration of liver malonyl-CoA (after meal ingestion) did not significantly differ between the fat-free and PUFA dietary treatments. Apparently PUFA feeding caused a coordinate decrease in the utilization and production of malonyl-CoA which resulted in no net change in malonyl-CoA pool size. Thus the mechanism by which PUFA suppresses fatty acid synthesis appears to be by coordinately and specifically reducing the amount of carboxylase and fatty acid synthetase.

Acetyl-CoA Carboxylase↗
PubMed1980

Polymer-protomer transition of acetyl-CoA carboxylase occurs in vivo and varies with nutritional conditions.

The protomeric form of purified acetyl coenzyme A carboxylase is inactivated by the binding of avidin to the biotinyl prosthetic group; the catalytically active filamentous form of the enzyme is resistant to avidin. This differential sensitivity to avidin was used to examine the influence of nutritional state on the proportion of polymeric and protomeric carboxylase occurring in avian liver. Hepatic carboxylase was 80% avidin-resistant (polymeric) in the fed chick. Food deprivation for 2 and 6 h reduced the avidin resistance to 54% and 30%, respectively. Similarly, within 1 h after fat intubation, the fraction of polymeric carboxylase had significantly decreased. Accompanying the change in carboxylase transformation was a comparable reduction in 3H2O incorporation into liver fatty acid. These data indicate that the protomer-polymer transition defined for purified acetyl-CoA carboxylase also occurs with the enzyme in vivo and that a lower polymer/protomer ratio is associated with reduced rates of fatty acid synthesis.

Acetyl-CoA Carboxylase↗
PubMed1980

Occupational therapy for the limb-deficient child: a developmental approach to treatment planning and selection of prostheses for infants and young children with unilateral upper extremity limb deficiencies.

Habilitation of the upper extremity limb-deficient child is enhanced when the treatment program is based on normal growth and development guidelines. Specific developmental tasks have been identified as key indicators of a child's readiness to benefit from prosthetic fitting, activation of major components, use training, and changes in prosthetic design such as modular prostheses and electric components. Use of developmental guidelines also enhances family support because their role in the program can be realistically defined and supported.

Arm↗
PubMed1979

Acute control of fatty acid synthesis by cyclic AMP in the chick liver cell: possible site of inhibition of citrate formation.

Glucagon and N,(6)O(2)-dibutyryl cyclic adenosine 3',5'-cyclic monophosphate (Bt(2)cAMP) inhibit fatty acid synthesis from acetate by more than 90% and prevent citrate formation in chick hepatocytes metabolizing glucose. With substrates that enter glycolysis at or below triose-phosphates, e.g., fructose, lactate, or pyruvate, Bt(2)cAMP has no effect on the citrate level and its inhibitory effect on fatty acid synthesis is substantially reversed. Because acetyl-CoA carboxylase requires a tricarboxylic acid activator for activity, it is proposed that regulation of fatty acid synthesis by Bt(2)cAMP is due, in part, to changes in the citrate level. Reduced citrate formation appears to result from a cAMP-induced inhibition of glycolysis. Bt(2)cAMP inhibits (14)CO(2) production from [1-(14)C]-, [6-(14)C]-, and [U-(14)C]glucose and has little effect on (14)CO(2) formation from [1-(14)C]- or [2-(14)C]pyruvate or from [1-(14)C]fructose. [(14)C]Lactate formation from glucose is depressed 50% by Bt(2)cAMP. In the presence of an inhibitor of mitochondrial pyruvate transport lactate accumulation is enhanced, but continues to be lowered 50% by Bt(2)cAMP. The activity of phosphofructokinase is greatly decreased in Bt(2)cAMP-treated cells while the activities of pyruvate kinase and acetyl-CoA carboxylase are unaffected. It appears that decreased glycolytic flux and decreased citrate formation result from depressed phosphofructokinase activity. Fatty acid synthesis from [(14)C]acetate is partially inhibited by Bt(2)cAMP in the presence of fructose, lactate, and pyruvate despite a high citrate level. Incorporation of [(14)C]fructose, [(14)C]pyruvate, or [(14)C]lactate into fatty acids is similarly depressed by Bt(2)cAMP. Synthesis of cholesterol from [(14)C]acetate or [2-(14)C]pyruvate is unaffected by Bt(2)cAMP. These results implicate a second site of inhibition of fatty acid synthesis by Bt(2)cAMP that involves the utilization, but not the production, of cytoplasmic acetyl-CoA.-Clarke, S. D., P. A. Watkins, and M. D. Lane. Acute control of fatty acid synthesis by cyclic AMP in the chick liver cell: possible site of inhibition of citrate formation.

Animals↗