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At least 19 recordsLinked to original sources
PubMed1969

Changes in the concentrations of hepatic metabolites on administration of dihydroxyacetone or glycerol to starved rats and their relationship to the control of ketogenesis.

1. Glycerol and dihydroxyacetone, both antiketogenic and readily metabolized, but differing in their effects on the redox state of the hepatic NAD couples, were given to starved rats and the contents of metabolites were measured in freezeclamped liver and in the blood. The object was to study the effects of changes in the redox state and of the availability of oxidizable substrates on the rate of ketone-body formation. 2. Intramuscular administration of dihydroxyacetone, glycerol or glucose to starved rats decreased the concentrations of acetoacetate and 3-hydroxybutyrate in the blood by 70-80% within 60min., whereas there was no major change in the free fatty acid concentration. 3. Dihydroxyacetone, but not glucose or glycerol, caused an immediate and sustained twofold increase in the blood lactate concentration. 4. Dihydroxyacetone and glycerol caused a rapid fall in the hepatic concentrations of ketone bodies, dihydroxyacetone being more effective. 5. This decrease was not accompanied by significant changes in the concentrations of acetyl-CoA, long-chain acyl-CoA or free CoA. 6. The hepatic glycerophosphate concentration rose about 40-fold on administration of glycerol, whereas with dihydroxyacetone the increase was only about 50%. The large increase in glycerophosphate concentration after administration of glycerol was completely prevented by pretreatment of the rats with tri-iodothyronine. Triiodothyronine-treated rats showed the same decrease in ketone-body concentrations after administration of glycerol as the untreated rats. 7. Glycerol and dihydroxyacetone caused an increase in the hepatic lactate concentration; the pyruvate concentration rose only after injection of dihydroxyacetone. 8. Both compounds increased liver glycogen. 9. Calculation of the [free NAD(+)]/[free NADH] ratios indicated that dihydroxyacetone increased the ratio in cytoplasm and mitochondria, whereas glycerol caused a prompt fall in both compartments, followed at 10min. by a slight rise in the mitochondrial compartment. 10. Dihydroxyacetone did not alter the hepatic content of ATP. 11. The findings suggest that the main reason for the antiketogenic effect of glycerol and dihydroxyacetone was a consequence of their ready metabolism and the provision of an increased supply of C(3) intermediates for conversion into oxaloacetate. Under the test conditions, neither the hepatic content of alpha-glycerophosphate nor the redox state of the NAD couples appeared to play a major role in the regulation of ketogenesis.

Acetoacetates↗
PubMed1985

Alkyl dihydroxyacetone phosphate synthase in human fibroblasts and its deficiency in Zellweger syndrome.

The cerebro-hepato-renal (Zellweger) syndrome is an autosomal recessive disorder biochemically characterized by the absence of morphologically distinguishable peroxisomes. Key enzymes involved in the biosynthesis of ether phospholipids, i.e., dihydroxyacetone phosphate acyltransferase and alkyl dihydroxyacetone phosphate synthase, are located in mammalian (micro)peroxisomes. We have previously shown a strikingly reduced activity of dihydroxyacetone phosphate acyltransferase in liver, brain, and cultured skin fibroblasts from Zellweger patients (Schutgens et al. 1984. Biochim. Biophys. Res. Commun. 120: 179-184). We have now extended these investigations by studying alkyl dihydroxyacetone phosphate synthase in cultured human skin fibroblasts. Enzymatic activity was determined by measuring the formation of radioactive alkyl dihydroxyacetone phosphate from palmitoyl dihydroxyacetone phosphate and [1-14C]hexadecanol as substrates. The enzyme was optimally active at pH 8.5 and was stimulated (about 2-3-fold) by the presence of 0.05% (v/v) Triton X-100. The apparent KM values for the enzyme in control fibroblasts amounted to 35 microM for palmitoyl dihydroxyacetone phosphate and 90 microM for hexadecanol. The reaction became inhibited at higher concentrations of both Triton X-100 and palmitoyl dihydroxyacetone phosphate. Control skin fibroblasts showed alkyl dihydroxyacetone phosphate synthase activity of 69 +/- 28 pmol X min-1 X mg-1 (n = 7), while fibroblasts from patients had an activity of only 6.3 +/- 1.7 pmol X min-1 X mg-1 (n = 7). Alkyl dihydroxyacetone phosphate synthase was also found to be deficient in tissue homogenates of Zellweger patients. The specific activity of this enzyme in liver, kidney, and brain homogenates from Zellweger patients was less than 15% of that in the corresponding tissues from controls.

Abnormalities, Multiple↗
PubMed1986

Stimulation of dihydroxyacetone and glycerol kinase activity in Streptococcus faecalis by phosphoenolpyruvate-dependent phosphorylation catalyzed by enzyme I and HPr of the phosphotransferase system.

Recently we reported the phosphoenolpyruvate (PEP)-dependent phosphorylation of a 55-kilodalton protein of Streptococcus faecalis catalyzed by enzyme I and histidine-containing protein (HPr) of the phosphotransferase system (J. Deutscher, FEMS Microbiol. Lett. 29:237-243, 1985). The purified 55-kilodalton protein was found to exhibit dihydroxyacetone kinase activity. Glycerol was six times more slowly phosphorylated than dihydroxyacetone. The Kms were found to be 0.7 mM for ATP, 0.45 mM for dihydroxyacetone, and 0.9 mM for glycerol. PEP-dependent phosphorylation of dihydroxyacetone kinase stimulated phosphorylation of both substrates about 10-fold. Fructose 1,6-diphosphate at concentrations higher than 2 mM inhibited the activity of phosphorylated and unphosphorylated dihydroxyacetone kinase in a noncompetitive manner. The rate of PEP-dependent phosphorylation of dihydroxyacetone kinase was about 200-fold slower than the phosphorylation rate of III proteins (also called enzyme III or factor III), which so far have been considered the only phosphoryl acceptors of histidyl-phosphorylated HPr. P-Dihydroxyacetone kinase was found to be able to transfer its phosphoryl group in a backward reaction to HPr. Following [32P]PEP-dependent phosphorylation and tryptic digestion of dihydroxyacetone kinase, we isolated a labeled peptide composed of 37 amino acids, as determined by amino acid analysis. The single histidyl residue of this peptide most likely carries the phosphoryl group in phosphorylated dihydroxyacetone kinase.

Bacterial Proteins↗
PubMed1976

Rates and properties of endogenous cyclic photophosphorylation of isolated intact chloroplasts measured by CO2 fixation in the presence of dihydroxyacetone phosphate.

1. Dihydroxyacetone phosphate in concentrations greater than or equal to 2.5 mM completely inhibits CO2-dependent O2 evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of Pi, but not by addition of 3-phosphoglycerate. In the absence of Pi, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the 14C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70-95%. Based on these results the mechanism of the inhibition of O2 evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts. 2. Although O2 evolution is completely suppressed by dihydroxyacetone phosphate, CO2 fixation takes place in air with rates of up to 65 mu mol-mg1 chlorophyll-h1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation. 3. Under anaerobic conditions, the rates of CO2 fixation in presence of dihydroxyacetone phosphate are low (2.5-7 mumol-mg1 chlorophyll-h1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2-10(-7) M) reaching values of up to 60 mumol-mg1 chlorophyll-h1. As under these conditions the ATP necessary for CO2 fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO2 fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded t-at only under anaerobic conditions an "overreduction" of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5-10(-7) M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO2 fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO2 fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation. 4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO2 fixation in presence of dihydroxyacetone phoshate by dibromothymoquinone under anaerobic conditions indicated that plastoquinone is an indispensible component of the endogenous cyclic electron pathway.

Carbon Dioxide↗
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↗
PubMed1976

Evidence for lipid synthesis by the dihydroxyacetone phosphate pathway in rabbit lung subcellular fractions.

Lipid synthesis by the lung requires a 3-carbon skeleton that can be provided by sn-glycerol-3-phosphate derived from glycolysis. This study investigated whether acylation of dihydroxyacetone-phosphate can serve as an alternate pathway for lung lipid synthesis. Rabbit lung microsomal and mitochondrial fractions were incubated with radiolabelled sn-glycerol-3-P and/or dihydroxyacetone-P. Palmitoyl CoA was used as acyl donor. The lipid fraction was subsequently isolated and radioactive incorporation was determined. Glycerol-3-P and dihydroxyacetone-P were both incorporated into the lipid fraction when each substrate was present alone. During incubation in the presence of equimolar concentrations of both substrates dihydroxyacetone-P accounted for 41 per cent of the total incorporation. These results show that acylation of dihydroxyacetone phosphate is a potential alternate to the glycerol-3-phosphate pathway for lung lipid synthesis.

Animals↗
PubMed1976

The glycerol phosphate, dihydroxyacetone phosphate and monoacylglycerol pathways of glycerolipid synthesis in rat adipose-tissue homogenates.

1. Fat-free homogenates from the epididymal fat-pads of rats were used to measure the rate of palmitate esterification with different substrates. The effectiveness of the acyl acceptors decreased in the order glycerol phosphate, dihydroxyacetone phosphate, 2-octadecenyl-glycerol and 2-hexadecylglycerol. 2. Glycerol phosphate and dihydroxyacetone phosphate inhibited their rates of esterification in a mutually competitive manner. 3. The esterification of glycerol phosphate was also inhibited in a partially competitive manner by 2-octadecenylglycerol and to a lesser extent by 2-hexadecylglycerol. However, glycerol phosphate did not inhibit the esterification of 2-octadecenylglycerol. 4. The esterification of dihydroxyacetone phosphate and 2-hexadecylglycerol was more sensitive to inhibition by clofenapate than was that of glycerol phosphate. Norfenfluramine was more effective in inhibiting the esterification of 2-hexadecylglycerol than that of glycerol phosphate or dihydroxyacetone phosphate. 5 It is concluded that rat adipose tissue can synthesize glycerolipids by three independent routes.

Acyltransferases↗
PubMed1976

Hormonal control of [14C]glucose synthesis from [U-14C]dihydroxyacetone and glycerol in isolated rat hepatocytes.

The hormonal control of [14C]glucose synthesis from [U-14C-A1dihydroxyacetone was studied in hepatocytes from fed and starved rats. In cells from fed rats, glucagon lowered the concentration of substrate giving half-half-maximal rates of incorporation while it had little or no effect on the maximal rate. Inhibitors of gluconeogenesis from pyruvate had no effect on the ability of the hormone to stimulate the synthesis of [14C]glucose from dihydroxyacetone. The concentrations of glucagon and epinephrine giving half-maximal stimulation from dihydroxacetone were 0.3 to 0.4 mM and 0.3 to 0.5 muM, respectively. The meaximal catecholamine stimulation was much less than the maximal stimulation by glucagon and was mediated largely by the alpha receptor. Insulin had no effect on the basal rate of [14C]clucose synthesis but inhibited the effect of submaximal concentration of glucagon or of any concentration of catecholamine. Glucagon had no effect on the uptake of dihydroxyacetone but suppressed its conversion to lactate and pyruvate. This suppression accounted for most of the increase in glucose synthesis. In cells from gasted rats, where lactate production is greatly reduced and the rate of glucose synthesis is elevated, glucagon did not stimulate gluconeogenesis from dihydroxyacetone. Findings with glycerol as substrate were similar to those with dihyroxyacetone. Ethanol also stimulated glucose production from dihydroxyacetone while reducing proportionately the production of lactate. Ethanol is known to generate reducing equivalents fro clyceraldehyde-3-phosphate dehydrogenase and presumably thereby inhibits carbon flux to lactate at this site. Its effect was additive with that of glucagon. Estimates of the steady state levels of intermediary metabolites and flux rates suggested that glucagon activated conversion of fructose diphosphate to fructose 6-phosphate and suppressed conversion of phosphoenolpyruvate to pyruvate. More direct evidence for an inhibition of pyruvate kinase was the observation that brief exposure of cells to glucagon caused up to 70% inhibition of the enzyme activity in homogenates of these cells. The inhibition was not seen when the enzyme was assayed with 20 muM fructose diphosphate. The effect of glucagon to lower fructose diphosphate levels in intact cells may promote the inhibition of pyruvate kinase. The inhibition of pyruvate kinase may reduce recycling in the pathway of gluconeogenesis from major physiological substrates and probably accounts fromsome but not all the stimulatory effect of glucagon.

Animals↗
PubMed1986

Acyl-CoA:dihydroxyacetone phosphate acyltransferase in human skin fibroblasts: study of its properties using a new assay method.

In relation to the finding that human skin fibroblasts are capable of de novo either phospholipid biosynthesis, we have studied the properties of acyl-CoA:dihydroxyacetone phosphate acyltransferase in fibroblast homogenates using a new assay method. The results indicate that the acylation of dihydroxyacetone phosphate shows an optimum at pH 5.5 with a broad shoulder of activity up to pH 6.4 and a decline in activity up to pH 8.2. At pH 5.5 the acyltransferase accepts dihydroxyacetone phosphate, but not glycerol 3-phosphate as a substrate. Furthermore, the transferase activity was found to be membrane-bound and inactivated by Triton X-100 at concentrations above 0.025% (w/v). Similar properties have been described for the enzyme as present in rat-liver and guinea-pig liver peroxisomes. These data, together with the finding that acyl-CoA:dihydroxyacetone phosphate acyltransferase is deficient in cultured skin fibroblasts from patients without peroxisomes (Zellweger syndrome), suggest that in cultured skin fibroblasts the enzyme is primarily located in peroxisomes.

Acyltransferases↗
PubMed1971

Dihydroxyacetone phosphate. Its structure and reactivity with -glycerophosphate dehydrogenase, aldolase and triose phosphate isomerase and some possible metabolic implications.

1. Dihydroxyacetone phosphate exists in neutral aqueous solution at 20 degrees C as a mixture of keto, gem-diol and enolic forms in the ratio 55:44:1. 2. The three forms are freely interconvertible and rate constants for these reactions have been determined. 3. Keto-dihydroxyacetone phosphate is the primary reactive species in the reactions catalysed by alpha-glycerophosphate dehydrogenase, aldolase and triose phosphate isomerase. 4. The proportion of keto form to gem-diol forms of dihydroxyacetone phosphate is temperature-dependent. At 37 degrees C, 83% is keto-dihydroxyacetone phosphate. 5. The enzymological and metabolic consequences of these results are discussed.

Acetone↗
PubMed1973

The tritium isotope effect of sn-glycerol 3-phosphate oxidase and the effects of clofenapate and N-(2-benzoyloxyethyl)norfenfluramine on the esterification of glycerol phosphate and dihydroxyacetone phosphate by rat liver mitochondria.

1. Owing to a (3)H isotope effect, the mitochondrial sn-glycerol 3-phosphate oxidase (EC 1.1.99.5) had a mean activity which was 8.4 times less with sn-[2-(3)H]-rather than with sn-[1-(14)C]glycerol 3-phosphate as a substrate. 2. A method for measuring the simultaneous synthesis of lipid from glycerol phosphate and dihydroxyacetone phosphate in rat liver mitochondria is described. 3. The lipid synthesized by rat liver mitochondria from sn-[1-(14)C]glycerol 3-phosphate was mainly phosphatidate and lysophosphatidate, whereas that synthesized from dihydroxy[1-(14)C]acetone phosphate was mainly acyldihydroxyacetone phosphate. 4. Additions of NADPH facilitated the conversion of acyldihydroxyacetone phosphate into lysophosphatidate and phosphatidate. 5. Hydrazine (1.4mm) or KCN (1.4mm) inhibited the synthesis of lipids from dihydroxyacetone phosphate but not from glycerol phosphate. 6. Clofenapate (1-2.5mm) inhibited the synthesis of lipids from dihydroxyacetone phosphate but slightly stimulated synthesis from glycerol phosphate. 7. The methanesulphonate of N-(2-benzoyloxyethyl)norfenfluramine, at 0.25-0.75mm, inhibited lipid synthesis from both glycerol phosphate and dihydroxyacetone phosphate.

Acetone↗
PubMed1985

Dihydroxyacetone synthase is an abundant constituent of the methanol-induced peroxisome of Candida boidinii.

Methylotrophic yeasts induce large peroxisomes when grown on methanol. The recent ability to stabilize and isolate these peroxisomes at pH 5.5 has led to the demonstration that two polypeptides comprise the bulk of the peroxisome of Candida boidinii, alcohol oxidase, and a 79-kDa species, determined by sodium dodecyl sulfate-polyacrylamide electrophoresis (Goodman, J.M., Scott, C.W., Donahue, P.N., and Atherton, J.P. (1984) J. Biol. Chem. 259, 8485-8493). The 79-kDa peroxisomal protein is now identified as dihydroxyacetone synthase, the first enzyme in the assimilatory pathway of formaldehyde utilization. This identification is based on several criteria: The enzyme activity is mainly in a particulate fraction at pH 5.5 but not at pH 8.0. It copurifies with alcohol oxidase and catalase on sucrose gradients. The 79-kDa protein behaves as a 135,000-kDa dimer on gel filtration, similar to the published behavior of the enzyme. The specific activity of dihydroxyacetone synthase in the pure 79-kDa preparation (3.20 units/mg of protein) is close to that reported for the purified enzyme (3.88 units/mg of protein). Antibodies against dihydroxyacetone synthase were used to show that its synthesis, induction, and assembly are similar to that of alcohol oxidase. Neither contains a detectable cleaved leader sequence and both are assembled post-translationally. The localization of dihydroxyacetone synthase to the peroxisome may influence the regulation of the two pathways of formaldehyde utilization and may protect the cell from damage by formaldehyde.

Aldehyde-Ketone Transferases↗
PubMed1989

Effect of glycerol and dihydroxyacetone on hepatic lipogenesis.

Glycerol is a dietary component which is metabolized primarily by the liver and kidney where it is used mainly for glucose synthesis. The metabolism of glycerol is very similar to that of dihydroxyacetone which can be considered its more oxidized counterpart. The effects of these substrates on hepatic lipogenesis and gluconeogenesis were examined. In isolated hepatocytes, 10 mM dihydroxyacetone caused a large increase in glucose output and stimulated lipogenesis without affecting the lactate/pyruvate ratio or the total ATP content of the cells. (As compared to dihydroxyacetone, 10 mM glycerol was less effective as a gluconeogenic substrate, increased the lactate/pyruvate ratio, caused a slight decrease in the total ATP content, and inhibited lipogenesis by at least 40% depending on the type of diet fed to the rats.) The fall in ATP levels was very small and did not correlate with the changes in fatty acid synthesis. The immediate cause of the inhibition of lipogenesis, brought about by glycerol in hepatocytes from sucrose fed rats, seemed to be a large decrease in pyruvate levels. This did not result from impairment of glycolysis but from a rise in the cytosolic NADH/NAD ratio.

3-Hydroxybutyric Acid↗
PubMed1977

The effect of dihydroxyacetone phosphate and 3-phosphoglycerate on O2 evolution and on the levels of ATP, ADP and Pi in isolated intact chloroplasts.

Addition of dihydroxyacetone phosphate (2.5 mM) or 3-phosphoglycerate (2.5 mM) to a suspension of isolated intact chloroplasts, which contains Pi only in low concentrations (0.2 mM) leads to a competitive inhibition of Pi uptake in the light. In consequence, the ATP/ADP ratio is strongly decreased. The rate of O2 evolution is also reduced under these conditions, but the degree of inhibition is much higher after addition of dihydroxyacetone phosphate than after addition of 3-phosphoglycerate. Therefore, besides the competitive inhibition of Pi uptake, additional effects of dihydroxyacetone phosphate and 3-phosphoglycerate on O2 evolution and CO2 fixation of isolated intact chloroplasts must occur, which are discussed.

Adenosine Diphosphate↗
PubMed1985

Pancreatic islets synthesize phospholipids de novo from glucose via acyl-dihydroxyacetone phosphate.

There is considerable evidence that an increased turnover of phosphoinositides and phosphatidic acid accompanies stimulus-induced insulin release. As glucose metabolism via glycolysis produces precursors for phospholipid synthesis, the time course of incorporation of [U14C] labelled glucose was measured to determine the pathways of triose carbon incorporation into phospholipids in the islet. Cultured islets were stimulated with glucose 2.7 or 33 mM. The labelled phospholipids present after stimulation were acyldihydroxyacetone phosphate, lysophosphatidic acid, phosphatidic acid and phosphatidylinositol. Acyl-dihydroxyacetone phosphate rose promptly within 1 minute of raising the glucose concentration and was the primary acylated triose labelled during the first 15 minutes. It was possible to show in vitro conversion of [U14C] glucose-derived acyl-dihydroxyacetone phosphate to lysophosphatidic acid and phosphatidic acid in the presence of NADPH (100 microM), indicating the presence in the islet of acyl-dihydroxyacetone phosphate: NADP oxidoreductase and acyl CoA:1 acylglycerol-3-phosphate acyl transferase, respectively. This study suggests that de novo synthesis of phosphatidic acid provides a link between glucose metabolism and the release of insulin.

Animals↗
PubMed1986

Inhibition of lipid accumulation and enhancement of energy expenditure by the addition of pyruvate and dihydroxyacetone to a rat diet.

To assess the effects of oral intake of pyruvate and dihydroxyacetone on body composition and metabolism, rats were divided into two groups and pair-fed one of the following isocaloric diets for 112 days. The control diet was a liquid diet with the following caloric composition: 14% protein, 28% fat, and 58% carbohydrate. The experimental diet was the same as the control diet except for the partial substitution of carbohydrate content with pyruvate and dihydroxyacetone. Rats receiving the experimental diet gained less weight than rats receiving the control diet. This reduction in body weight appeared to be largely the result of inhibition of lipid accumulation. The experimental diet reduced body fat content by 32% without any significant effect on either protein or water content. Rats receiving the experimental diet did not have increased loss of calories in the stool, but had greater rates of heat production and energy expenditure, which was accompanied by an elevated plasma level of thyroxine. Furthermore, rats receiving the experimental diet had a smaller rate of lipid synthesis in their adipose tissue, and a reduced plasma insulin level. The data suggest that inhibition of gain in weight with the addition of pyruvate and dihydroxyacetone to the diet is the result of an increased loss of calories as heat at the expense of storage as lipid.

Administration, Oral↗
PubMed1979

Subcellular localization of acyl coenzyme A: dihydroxyacetone phosphate acyltransferase in rat liver peroxisomes (microbodies).

Upon differential centrifugation of rat liver homogenate, the enzyme acyl-CoA:dihydroxyacetone-phosphate acyltransferase (EC 2.3.1.42) was found to be localized in the light mitochondrial (L) fraction which is enriched with lysosomes and peroxisomes. Peroxisomes were separated from lysosomes in a density gradient centrifugation using rats which were injected with Triton WR 1339. By comparing the enzyme distribution with the distribution of different marker enzymes, it was concluded that dihydroxyacetone phosphate acyltransferase is primarily localized in rat liver peroxisomes (microbodies). Similarly, the enzyme acyl dihydroxyacetone-phosphate:NADPH oxidoreductase (EC 1.1.1.101) was shown to be enriched in the peroxisomal fraction, although a portion of this reductase is also present in the microsomal fraction.

Acyltransferases↗
PubMed1977

Properties of dihydroxyacetone phosphate acyltransferase in the harderian gland.

We have used a microsomal preparation from the pink portion of the rabbit harderian gland to study the properties of dihydroxyacetone-P acyltransferase. The enzymatic activity in the microsomes is latent and is stimulated approximately 20-fold by the addition of detergent to the assay system. Both deoxycholate and cholate stimulated the enzyme at concentrations considerably below the critical micellar concentration of these detergents. The acyltransferase was not solubilized by treatment with these detergent concentrations. In addition, we have shown that the acyltransferase is sensitive to proteolytic digestion in the presence of deoxycholate concentrations that render the microsomal vesicles permeable to the protease, but is insensitive to the protease treatment in the absence of detergent. Collectively, these data indicate that the active site of dihydroxyacetone-P acyltransferase is exposed to the lumenal surface of the microsomal vesicles. This enzyme is distinct from the glycerol-P acyltransferase in that the dihydroxyacetone-P acyltransferase is sensitive to protease digestion only in the presence of deoxycholate, is not inhibited by sulfhydryl reagents, and is not competitively inhibited by sn-glycerol-3-P.

Acyltransferases↗