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R J Pollock

Publications and source records attributed to R J Pollock.

14 recordsLinked to original sources
PubMed1990

Dependence of an alkyl glycol-ether monooxygenase activity upon tetrahydropterins.

Glyceryl-ether monooxygenase (1-alkyl-sn-glycerol,tetrahydropteridine: oxygen oxidoreductase, EC 1.14.16.5) catalyzes the oxidative cleavage of 1-O-alkyl glycerol or glycol derivatives to a long-chain aldehyde and the glycerol or glycol derivative. The specificity for tetrahydropterins of a similar, perhaps identical, enzyme that cleaves O-hexadecyl ethylene glycol in rat liver microsomes was examined with the use of an assay based on [1-3H]ethylene glycol formation from 2-hexadecyloxy [1-3H]ethan-1-ol. Several tetrahydropterin derivatives are effective electron donors for this reaction, and 2,4,5-triamino-6-hydroxypyrimidine is somewhat effective, but NADH, NADPH, ascorbate, reduced dichlorophenolindophenol and glutathione are inactive. Tetrahydropterin derivatives differ from each other in apparent Km and apparent Vmax. The order of increasing apparent Km values is tetrahydropterin approximately 6-methyltetrahydropterin approximately tetrahydrobiopterin less than 6.7-dimethyltetrahydropterin less than tetrahydrofolate. The order of increasing apparent Vmax values is tetrahydrofolate approximately tetrahydropterin less than 6-methyltetrahydropterin approximately tetrahydrobiopterin approximately 6,7-dimethyltetrahydropterin. Results obtained with the use of a spectrophotometric assay, in which tetrahydropterin oxidation is coupled to NADH oxidation by dihydropteridine reductase (NAD(P)H: 6,7-dihydropteridine oxidoreductase, EC 1.6.99.7), indicated that the ratio of 6,7-dimethyltetrahydropterin or 6-methyltetrahydropterin oxidized to ether lipid degraded is about 1.1 to 1.3. Unlike cytochrome P-450-dependent hydroxylases, this alkyl glycol-ether monooxygenase is not inhibited by carbon monoxide. 1-O-hexadecyl-rac-glycerol (chimyl alcohol) competitively inhibits the oxidation of the glycol ether indicating that the same enzyme probably catalyzes the oxidation of both O-alkyl glycol and 1-O-alkyl glycerol.

Alcohols↗
PubMed1981

Effect of cyclic AMP-dependent protein phosphorylating conditions on the pH-dependent activity of tyrosine hydroxylase from beef and rat striata.

Tyrosine hydroxylase (TH, EC 1.14.16.2) from beef brain striata was purified 23-fold from an extract of an acetone powder. If this enzyme preparation is treated with a cyclic AMP[-dependent protein phosphorylation system, there is a change in the pH dependence of the enzyme activity. The pH optimum at saturating tetrahydrobiopterin (BH4) concentration is shifted from below pH 6 to about pH 6.7. At pH 7, activation is expressed mainly as an increase in Vmax, whereas at pH 6, activation is expressed mainly as a decrease in Km for the pterin cofactor. Further, even with the control enzyme the Km for pterin cofactor declines precipitously as the pH is increased from 6 toward neutrality. Similar data were obtained with G-25 Sephadex-treated rat striatal TH. Experiments in which rat striatal synaptosomes were used demonstrated that the in situ activation of TH by phosphorylating conditions is expressed primarily as an increase in the maximum rate of dopamine synthesis. These results indicate that changes in TH activity caused by cyclic AMP-dependent protein phosphorylation will depend to a large extent on the pH of the TH environment.

Animals↗
PubMed1976

Incorporation of D-[3-3H, U-14C] glucose into glycerolipid via acyl dihydroxyacetone phosphate untransformed and viral-transformed BHK-21-c13 fibroblasts.

Untransformed BHK-21-c13 fibroblasts as well as 4 polyoma-transformed strains were incubated with D-[U-14C,3-3H]glucose. This substrate generates intracellular labeled glycerol, and also [4-3H]NADPH via the phosphogluconate oxidative pathway. The latter selectively transfers hydrogen to C-2 of glycerol in glycerolipid via the acyl dihydroxyacetone phosphate pathway. After incubation, the distribution of radioactivity and the ratios of 3H/14C at the three positions of recovered glycerol were determined in sn-glycerol 3-phosphate, saponifiable glycerolipids, alkyl ether glycerolipids, and plasmalogens. In each of the cell types examined, 3H in the sn-1 position of glycerol in the recovered ether-containing glycerolipids was negligible, yet this position contained most of the recovered 3H in sn-glycerol 3-phosphate and saponifiable glycerolipids. The 3H/14C ratio in position 2 of glycerol, measured at various incubation times, was from 5- to 200-fold greater in the saponifiable glycerolipids than in free sn-glycerol 3-phosphate. The ratio in position 2 of ether-containing glycerolipids was the same or greater than that in the saponifiable glycerolipids in all of the cell types employed. A similar pattern in the 3H/14C ratio was observed when BHK-21-c13 cells were incubated with D-[U-14C,1-3H]glucose. These observations demonstrate significant participation of the acyl dihydroxyacetone phosphate pathway in glycerolipid synthesis in BHK cells.

Cell Line↗
PubMed1975

The relative utilization of the acyl dihydroxyacetone phosphate and glycerol phosphate pathways for synthesis of glycerolipids in various tumors and normal tissues.

Rates of phosphatidate synthesis from dihydroxyacetone phosphate via acyl dihydroxyacetone phosphate or glycerol phosphate are compared in homogenates of 13 tissues, most of which are deficient in glycerol phosphate dehydrogenase (EC 1.1.1.8). In all tissues examined, dihydroxyacetone phosphate entered phosphatidate more rapidly via acyl dihydroxyacetone phosphate than via glycerol phosphate. Tissues with a relatively low rate of phosphatidate synthesis via glycerol phosphate, showed no compensating increase in the rate of synthesis via acyl dihydroxyacetone phosphate. The rates at which tissue homogenates synthesize phosphatidate from dihydroxyacetone phosphate via glycerol phosphate increase as glycerol phosphate dehydrongenase increase. Both glycerol phosphate dehydrogenase and glycerol phosphate: acyl CoA acyltransferase (EC 2.3.1.15) are more active than dihydroxyacetone phosphate : acyl CoA acyltransferase (EC 2.3.1.42). Thus, all the tissue homogenates possessed an apparently greater capability to synthesize phosphatidate via glycerol phosphate than via acyl dihydroxyacetone phosphate, but did not express this potential. This result is discussed in relation to in vivo substrate limitations.

Acyltransferases↗
PubMed1969

Periodontics.

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Adolescent↗