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Biomedical subjects

G Y Sun

Publications and source records attributed to G Y Sun.

At least 127 records · Page 7Linked to original sources
PubMed1984

Partial purification and properties of long-chain acyl-CoA hydrolase from rat brain cytosol.

Long-chain acyl-CoA hydrolase (EC 3.1.2.2) has been partially purified from the 100,000 X g supernatant fraction of rat brain tissue. The purification procedure included chromatography on gel filtration media, DEAE-cellulose, CM-cellulose, and hydroxyapatite. The partially purified enzyme had a specific activity of 7.1 mumol/min-mg, and when analyzed by polyacrylamide gel electrophoresis, revealed one major and three minor bands of protein in the presence of dodecyl sulfate and two major bands of protein in the absence of dodecyl sulfate. The enzyme had a molecular weight of 65,000 and showed no evidence of aggregated or dissociated forms. The highest catalytic activity was exhibited with palmitoyl-CoA and oleoyl-CoA as substrates. Lower activity was found with decanoyl-CoA as the substrate and little or no activity was found with acetyl-CoA, malonyl-CoA, butyryl-CoA, or acetoacetyl-CoA. The enzyme was inhibited by CoA, various metal ions, including Mn2+, Mg2+ and Ca2+, and by bovine serum albumin. Heating the enzyme produced a loss of activity which corresponded to a first-order kinetic process, the rate of which was independent of the choice of substrate used to measure enzyme activity. This finding supports the idea that the purification procedure yields a single species of long-chain acyl-CoA hydrolase.

Acyl Coenzyme A↗
PubMed1984

On the status of lysolecithin in rat cerebral cortex during ischemia.

Lysolecithin (lysoglycerophosphocholine, LPC) was isolated from rat cerebral cortex and quantitatively analyzed at various times after postdecapitative ischemic treatment. In addition, different procedures for extraction and analysis of the LPC in brain were evaluated. Results indicated that LPC can be quantitatively extracted into the organic phase using the conventional extraction procedure with chloroform-methanol (2:1, vol/vol). However, care should be taken to avoid using strong acids, which can hydrolyze the alkenylether side chain of the plasmalogens, resulting in the release of 2-acylphospholipids. Quantitative GLC analysis using myristoyl-LPC as internal standard revealed a level of 1.8 nmol LPC/mg protein in brain with acyl groups comprised mainly of 16:0, 18:0, and 18:1. The acyl group profile reflects that the LPC are derived mainly from phospholipase A2 action. An increase of 46% in the LPC level was observed at 1 min after ischemic treatment, but this was followed by a steady decline. Ischemia induced an increase in the LPC species that are enriched in 18:0 and 18:1 fatty acids. The transient appearance of LPC during ischemia further suggests that this phospholipid is undergoing active turnover, possibly hydrolysis by the lysophospholipase. This mechanism of action may account, at least in part, for the increase in both saturated and unsaturated fatty acids during the early phase of the ischemic treatment.

Animals↗
PubMed1983

Chronic ethanol administration induced an increase in phosphatidylserine in guinea pig synaptic plasma membranes.

Chronic ethanol administration to guinea pigs via intragastric intubation elicited a specific increase (50%) in phosphatidylserine in the synaptic plasma membrane. The ethanol-treated group also showed a 53% increase in synaptosomal (Na,K)-ATPase activity. Analysis of the acyl group composition of individual phospholipids in the same membrane fraction revealed only small changes which varied depending on the type of phospholipids. Since the (Na,K)-ATPase is known to be specifically activated by phosphatidylserine, the adaptive increase in enzyme activity during chronic ethanol treatment may be related to the increase in this type of negatively charged phospholipid.

Animals↗
PubMed1983

Acylation of lysoglycerophospholipids by adrenal membranes.

1. Substantial differences were found in the acyl donor and lyso-acceptor specificities among subcellular membranes and with respect to different regions of the adrenal gland. 2. In the presence of Mg2+-ATP and CoASH, adrenal microsomes were actively transferring arachidonate to lysophospholipids with acyl acceptor specificity in the order: 1-acyl-GPI greater than 1-acyl-GPC greater than 1-acyl-GP. However, when oleoyl-CoA was used, acyl acceptor specificity for the microsomal transferases was in the order: 1-acyl-GPC greater than 1-acyl-GP greater than 1-acyl-GPI. 3. Mitochondrial membranes had very low acyl transfer activity and they preferred 1-acyl-GPC over other lyso-acceptors. 4. The chromaffin granules were apparently lacking this type of activity.

Acyl Coenzyme A↗
PubMed1983

Detergent effects on the phosphatidylinositol-specific phospholipase C in rat brain synaptosomes.

In the presence of Ca2+ (2.5 mM) and using [14C]arachidonoyl phosphatidylinositol (PI) membrane as substrate, phosphatidylinositol-specific phospholipase C (PI-PLC) (EC 3.1.4.10) in rat brain synaptosomes was activated by deoxycholate but not taurocholate. Calcium stimulated enzymic hydrolysis by both detergents, but the stimulatory effect of taurocholate was less than that of deoxycholate. Peak stimulation for deoxycholate was observed at 1 mg/ml, whereas that for taurocholate was 4 mg/ml. When 1 mM EDTA was added to the taurocholate (4 mg/ml) and Ca2+ (3.5 mM) system, synaptosomal PI-PLC activity was greatly stimulated, to almost the same level as the deoxycholate + Ca2+ system. This system required the presence of all three factors, and EGTA could not effectively replace EDTA in the stimulatory action. The detergent-induced hydrolysis of synaptosomal PI by the deoxycholate + Ca2+ and the taurocholate + Ca2+ + EDTA systems was strongly inhibited by divalent metal ions such as Zn2+, Cu2+, Pb2+, and Fe2+, whereas Mg2+ and Ca2+ were ineffective. Nevertheless, only the deoxycholate + Ca2+ system was responsive to enzyme inhibition by membrane-perturbing agents such as lysophospholipids and free fatty acids. The specific requirement for EDTA in the taurocholate system may be due to the release of a pool of inhibitory divalent metal ions from the membranes.

Animals↗
PubMed1983

Serum albumin washing specifically enhances arachidonate incorporation into synaptosomal phosphatidylinositols.

Arachidonate incorporation into synaptosomal phospholipids was shown to be affected by factors including the procedure for preparation of the membrane fractions and preincubation of synaptosomes prior to assay of incorporation of arachidonate into both phosphatidylcholine (PC) and phosphatidylinositol (PI). However, the inhibition toward incorporation into PIs, but not PCs, was fully reversed when the membranes were washed with bovine serum albumin. A twofold increase in arachidonate incorporation into PIs was also observed when freshly prepared synaptosomes were washed with serum albumin immediately before assay of incorporation activity. The inhibitory action is thought to be due to an increase in polyunsaturated fatty acids and/or their oxidation products which may then elicit a special effect on the acyltransferase responsible for transferring arachidonate into phosphatidylinositols. The differences in fatty acid uptake and response to serum albumin also suggest the presence of different acyltransferase for acyl transfer to PIs and PCs.

Animals↗
PubMed1981

Effects of postdecapitative ischemia on arachidonate release from brain synaptosomes.

Synaptosomal phosphoglycerides were labeled after incubation with [1-14C]arachidonic acid, ATP, Mg2+, CoASH, and a small amount of 1-acylglycerophosphocholines. Under this incubation system, radioactivity was directed largely to diaclyglycerophosphocholines but diacylglycerophosphoinositols were also labeled to a lesser extent. Synaptosomes obtained after a 5-min ischemic treatment indicated a decrease (10-20%) in incorporation of radioactivity into the phospholipids. The ischemic synaptosomes also tended to retain a larger portion of the labeled arachidonate during the wash with bovine serum albumin. Upon incubation of the prelabeled synaptosomes in a sucrose-Tris (pH 7.4) medium at 37 degrees C, a time-dependent release of labeled arachidonate from the phospholipids was observed in both control and ischemic samples. Arachidonate release from the prelabeled synaptosomes was not affected by EDTA (1 mM) or taurocholate (0.4%) but was stimulated by Ca2+ (2.5 mM) or Ca2+ (3.5 mM) together with EDTA (1 mM). After incubation at 37 degrees C for 1 hr without added factors, the phospholipid degradation, as well as the appearance of free fatty acids, were higher in the ischemic samples (especially after 1 min of treatment) as compared to controls.

Animals↗
PubMed1981

Effects of acute hypoxia on incorporation of [1-14C]arachidonic into glycerolipids of rat brain.

The effects of 1 min of acute hypoxic treatment (1% O2 in N2) on incorporation of [1-14C]arachidonic acid into brain lipids of 16-day-old rats were investigated at 3, 6, and 12 min after intracerebral injection of the labeled fatty acid. The hypoxic-hypoxia condition associated with convulsive seizures caused a decrease in the conversion of labeled arachidonate to its acyl-CoA as well as incorporation of the label into the brain phospholipids. Among the phospholipids, there was a specific decrease in the labeling of diacylglycerophosphoinositol (GPI), and this change was accompanied by an increase in labeling of the diacylglycerols. These results indicate that metabolism of the long-chain fatty acids and some glycerolipids in brain are vulnerable to acute hypoxic treatment.

Animals↗
PubMed1981

Metabolism of oleoyl-CoA in rat brain synaptosomes: effects of calcium and post-decapitative ischemia.

The hydrolysis of acyl-CoA by acyl-CoA hydrolase (EC 3.1.2.2.) in brain synaptosomes was inhibited by calcium. This inhibition was partly due to interaction of Ca2+ with the acyl-CoA, which was present in the soluble form, and partly due to complex formation among acyl-CoA, Ca2+ and membrane phospholipids. The inhibition of acyl-CoA hydrolase activity, as well as the complex formation, could be reversed if incubation was carried out in the presence of Ca2+ chelating agents. Synaptosomes isolated from brain samples after 1 min of postdecapitative treatment showed a decrease in oleoyl-CoA hydrolase activity. The physiological implication of acyl-CoA metabolism in relation to synaptic function is discussed.

Acyl Coenzyme A↗
PubMed1981

Effects of acute administration of chlorinated water on liver lipids.

An acute administration of chlorinated water to rats caused "fatty liver" and indicated a more than 2-fold increase in liver triacylglycerols at 2 days after administration. The acyl group composition of triacylglycerols and phospholipids in both liver mitochondria and liver whole homogenate were also altered by the chlorine treatment. Among the phospholipid acyl groups, there was an increase in the proportion of 20:4 but a decrease in most other polyunsaturated acyl groups. The acyl group changes were more obvious with phosphatidylcholines than with phosphatidylethanolamines. Other phospholipids, including cardiolipin in the mitochondrial membranes, were not greatly altered. Both morphological and biochemical changes were maximum at 2 days after the treatment and were fully recovered after 10 days. The disturbance of a number of enzymatic processes in the liver membranes may account for a large part of the changes observed.

Animals↗
PubMed1981

Degradation of arachidonoyl-labeled phosphatidylinositols by brain synaptosomes.

Incubation of synaptosomes together with 1-acyl-2-[14C]arachidonoyl-sn-glycerophosphoinositols (GPI) and sodium deoxycholate yielded diacylglycerols and free arachidonic acid. Diacylglycerol formation is attributed to hydrolysis by the diacyl-GPI-specific phospholipase C (EC 3.1.4.10), and this reaction requires sodium deoxycholate for optimal activity. The free arachidonic acid formed is attributed to hydrolysis of diacyl-GPI by phospholipase A (EC 3.1.1.5). Free fatty acid release was observed during incubation, even in the absence of bile salts, but this process was preferentially stimulated by sodium taurocholate. The release of fatty acids was not specific for diacyl-GPI, as similar release was obtained during incubation with other phosphoglycerides. In the presence of deoxycholate (2 mg/ml), the release of diacylglycerols was maximal at a diacyl-GPI concentration around 1.0 mM. However, the free fatty acid release was linear with respect to the substrate at least up to 1.4 mM. The rate of diacylglycerol release from diacyl-GPI was more rapid in the initial 30 min, whereas the free fatty acid release was linear with time up to 2 h. Under this incubation condition, calcium was found to stimulate both types of hydrolytic action, although the concentration needed to achieve this stimulation was rather high. This type of labeled precursor is potentially useful for studies of the different modes of diacyl-GPI degradation by enzymes in brain subcellular membranes.

Animals↗
PubMed1981

Metabolism of acyl-CoA in the developing rat brain.

The enzymic hydrolysis of oleoyl-CoA in rat brain cytosol and the acyltransferase-mediated transfer of acyl-CoA to 1-acyl-glycerophosphates and 1-acyl-glycerophosphocholines by brain microsomes were examined at various stages of brain development. Although the amount of cytosolic protein (per gram weight) in brain decreased steadily with age during development, specific activity of the acyl-CoA hydrolase in this fraction increased nearly onefold during the first 2 weeks of age before exhibiting a steady decline until maturation. The amount of microsomes isolated from brain increased during the 1st week of age but started to decline steadily thereafter. Specific activity of the oleoyl-CoA transfer to 1-acylphospholipids by brain microsomes seemed to remain rather constant throughout the 1st month of age but they showed an increase at around 29 days of age before dropping to a steady level after reaching adult age.

Acyl Coenzyme A↗
PubMed1980

Effects of postdecapitative ischemia and hypoxia on the phosphoglyceride acyl groups of rat brain membranes.

Rats subjected to mild hypoxic and postdecapitative ischemic treatments indicated a decrease (8-16%) in the proportion of polyunsaturated acyl groups of diacyl glycerophosphocholines (diacyl-GPC), diacyl glycerophosphoethanolamines (diacyl-GPE), and alkenylacyl glycerophosphoethanolamines (alkenylacyl-GPE) in brain synaptosomes. In general, the acyl group changes due to mild hypoxic treatment were less obvious than those due to the ischemic treatment. The decrease in polyunsaturated acyl groups was marked by an increase in the saturated (16:0 and 18:0) and monoenoic (18:1) acyl groups. Among the polyunsaturated acyl groups, arachidonate (20:4) indicated the greatest decrease in response to ischemic and hypoxic treatments. The decrease in polyunsaturated fatty acids of diacyl glycerophosphocholines was largest in the first minute of ischemic treatment and the first 30 min of hypoxic treatment. After the initial decrease, there was a slight recovery. The biphasic type of change was thought to be due to active reacylation of the lyso phospholipids. This biphasic change, however, was not observed with ethanolamine phosphoglycerides which indicated a steady decrease in the polyunsaturated acyl group content with time of ischemic treatment. The increased hydrolysis of polyunsaturated acyl groups in brain membrane phosphoglycerides due to the ischemic and hypoxic treatments seemed to correlate well with the implication of phospholipase A(2) involvement in eliciting the increase in free fatty acids during brain stimulation.

Animals↗
PubMed1980

The kinetic properties of oleoyl-CoA:1-acyl-sn-glycero-3-phosphocholine O-acyltransferase from mouse-brain microsomes.

The kinetic properties of acylation of 1-acyl-sn-glycero(-3)phosphocholine by oleoyl-CoA were examined using mouse brain microsomes. The enzyme-catalyzed reactions were studied by measuring the rate of reaction while systematically varying the concentrations of oleoyl-CoA and 1-acylglycerophosphocholine. Double reciprocal plots of velocity versus 1-acylglycerophosphocholie produced a family of parallel lines and similar plots for oleoyl-CoA produced a family of parallel curves. Inhibition was observed at high concentrations of either substrate. By extrapolation from low substrate concentrations, the V for oleoyl-CoA:1-acylglycerophosphocholine acyltransferase in brain microsomes was found to be 6.1 nmol min-1 mg-1 and Km values were determined to be 11 microM and 107 microM for oleoyl-CoA and 1-acylglycerophosphocholine, respectively. Similar results were obtained for the enzyme-catalyzed transfer of oleoyl groups to 1-acyl-sn-glycerophosphoinositol. In this case, V was found to be 2.1 nmol min-1 mg-1 and the Km values were 4 microM and 14 microM for oleoyl-CoA and 1-acylglycerophosphoinositol, respectively. The mechanistic implications of the kinetic properties of the acyltransferases with respect to acyl group specificity for the phosphoglycerides in brain microsomes are discussed.

1-Acylglycerophosphocholine O-Acyltransferase↗