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PubMed1981

Effects of cell size and animal age on glucose metabolism in pig adipose tissue.

Adipose tissue slices were prepared from middle subcutaneous or perirenal adipose tissue excised from pigs of different ages (and obesity) and incubated with [U-14C]glucose. After incubation, the slices were fixed with osmium tetroxide and separated into diameter ranges of 20--63, 63--102, and 102--153 microgram, respectively. Following determination of cell size and number, the fixed adipocytes were decolorized with H2O2 prior to quantification of glucose conversion to total lipid, glyceride fatty acids, glycerideglycerol, and CO2. Glucose conversion to total lipid or CO2 was unaffected by the presence of purified porcine insulin (0, 10, 100, 1000, and 100,000 microM/ml). Within animals, adipocytes of different sizes were not different with regard to insulin sensitivity. Within a weight (age) group, conversion of glucose to total lipid (insulin present) or to glyceride fatty acids and glyceride-glycerol (insulin absent) per cell was significantly greater in large adipocytes compared to small adipocytes, regardless of the group examined. With increasing weight or age, there was a markedly decreased conversion of glucose to total lipid and glyceride fatty acids among adipocytes of similar size within a cell-size fraction. The diminution in glucose metabolism was greater (as a percentage) in 20--63 microgram adipocytes than for 63--102 or 102--153 microgram adipocytes. However, for all cell-size fractions there was a marked decrease in glucose conversion to fatty acids. Glyceride-glycerol synthesis was impaired in adipocytes from older pigs, but the decrease was less than observed for glyceride fatty acid synthesis.

Adipose Tissue↗
PubMed1976

On the mechanism of regulation of omega oxidation of fatty acids.

The stimulatory effect of starvation on omega oxidation of stearate by the 20,000 X g supernatant fluid of rat liver homogenates was studied. The effect was obtained after starvation for 24 hours. Starvation for longer times did not further increase omega oxidation. The stimulatory effect of starvation on omega oxidation of stearic acid was accompanied by a reduced incorporation of stearic acid into phosphatidic acid, diglycerides, and triglycerides. Substitution of the 100,000 X g supernatant fluid from liver homogenate of starved rats with 100,000 X g supernatant fluid from liver homogenates of control rats reduced the microsomal omega oxidation of stearic acid with a simultaneous increase in incorporation of stearic acid into the different glycerides. Under the latter conditions almost no free stearic acid could be isolated from the incubation mixture after the incubation. Of three different soluble factors necessary for glyceride formation, ATP appeared to be the most important from a regulatory point of view. Thus the soluble fraction of liver homogenate from a starved rat was shown to contain suboptimal concentrations of ATP. Addition of physiological amounts of ATP to the 20,000 X g supernatant fluid of homogenate of liver of starved rats had the same effect as addition of 100, 000 X g supernatant fluid from liver homogenate of control rats, i.e. decrease in omega oxidation and increase in formation of glycerides. Addition of sn-glycerol 3-phosphate and CoA-SH in amounts optimal for glyceride formation to the 20,000 X g supernatant fluid of liver homogenate of starved rats had only small effects on omega oxidation and glyceride formation. The results are consistent with a competition for free fatty acids between the acyl-CoA synthetases involved in biosynthesis of glycerides and the microsomal hydroxylase(s) involved in omega oxidation of fatty acids. The concentration of ATP in the soluble fraction is of importance in this competition. The possibility is discussed that this competition is of importance also under in vivo conditions and that a decreased rate of esterification in the starved state is responsible for the higher excretion of omega-oxidized fatty acids in urine in the ketotic state.

Animals↗
PubMed1978

Role of phospholipid in adrenaline-induced lipolysis and cyclic AMP production.

Lipid micelles consisting of a glyceride mixture (triolein, diolein, and monoolein) and lecithin bound adrenaline-14C more strongly than did micelles consisting of the glyceride mixture only. Lipid micelles consisting of the glyceride mixture and phosphatidic acid also bound adrenaline-14C effectivily, whereas lipid micelles consisting of the glyceride mixture and diglyceride, obtained from lecithin, did not bind the hormone strongly. Both phenoxybenzamine (an alpha- blocker) and propranolol (a beta-blocker) strongly inhibited the association between adrenaline-14C and lipid micelles consisting of the glyceride mixture and lecithin. Propranolol, inhibited adrenaline-induced lipolysis in both fat cells and fat globules, whereas, phenoxybenzamine, did not affect adrenaline-induced lipolysis. Both agents reduced adrenaline-induced adenyl-cyclase activation in fat cell ghosts. Phospholipid was also found to be related with adrenaline-mediated adenylcyclase activation.

Adenylyl Cyclases↗
PubMed1989

Influence of age and exercise training on lipid metabolism in Fischer-344 rats.

The influence of training on fatty acid and glyceride synthesis by liver and adipose tissue homogenates of young and old Fischer-344 rats was examined. Four groups of rats (10 animals/group) were studied: young untrained, young trained, old untrained, and old trained. Training of each group was for 10 wk at 75% maximal O2 uptake. Young rats were killed at 6 mo of age and old rats were killed at 27 mo of age. Fatty acid synthesis was assessed by measuring the activities of acetyl-CoA carboxylase, fatty acid synthase, ATP citrate-lyase, "malic" enzyme, and glucose-6-phosphate dehydrogenase. Glyceride synthesis was evaluated by determining the rate of incorporation of [14C]glycerol 3-phosphate into lipids. In addition, lipoprotein lipase activity was measured in acetone-ether powders of adipose tissue from the four groups of rats. In liver, training had no effect on fatty acid or glyceride synthesis in either group. However, aging caused a significant decrease in the activities of four of the lipogenic enzymes but had no effect on glyceride synthesis. Training caused an increase in fatty acid synthase and glyceride synthesis in adipose tissue, and aging decreased lipoprotein lipase activity. It was concluded that training enhances the synthetic capacity of lipids by adipose tissue but that aging had a more profound effect in that the activities of the enzymes involved in these processes were lower in the old rats. Furthermore, the decreased activity of lipoprotein lipase in the older rats may explain the higher plasma triglyceride levels that were observed in these animals.

ATP Citrate (pro-S)-Lyase↗
PubMed1974

Glucose metabolism and the response to insulin by human adipose tissue in spontaneous and experimental obesity. Effects of dietary composition and adipose cell size.

[1-(14)C]glucose oxidation to CO(2) and conversion into glyceride by adipose tissue from nonobese and obese subjects has been studied in vitro in the presence of varying medium glucose and insulin concentrations as functions of adipose cell size, the composition of the diet, and antecedent weight gain or loss. Increasing medium glucose concentrations enhance the incorporation of glucose carbons by human adipose tissue into CO(2) and glyceride-glycerol. Insulin further stimulates the conversion of glucose carbons into CO(2), but not into glyceride-glycerol. Incorporation of [1-(14)C]glucose into glyceride-fatty acids by these tissues could not be demonstrated under any of the conditions tested. Both adipose cell size and dietary composition influence the in vitro metabolism of glucose in, and the response to insulin by, human adipose tissue. During periods of ingestion of weight-maintenance isocaloric diets of similar carbohydrate, fat, and protein composition, increasing adipose cell size is associated with (a) unchanging rates of glucose oxidation and increasing rates of glucose carbon incorporation into glyceride-glycerol in the absence of insulin, but (b) decreasing stimulation of glucose oxidation by insulin. On the other hand, when cell size is kept constant, increasing dietary carbohydrate intake is associated with an increased basal rate of glucose metabolism and response to insulin by both small and large adipose cells. Thus, the rate of glucose oxidation and the magnitude of the insulin response of large adipose cells from individuals ingesting a high carbohydrate diet may be similar to or greater than that in smaller cells from individuals ingesting an isocaloric lower carbohydrate diet.The alterations in basal glucose metabolism and insulin response observed in adipose tissue from patients with spontaneous obesity are reproduced by weight gain induced experimentally in nonobese volunteers; these metabolic changes are reversible with weight loss. The relationships among adipose cell size, dietary composition, and the metabolism of adipose tissue are similar in spontaneous and in experimental obesity.

Adipose Tissue↗
PubMed1988

Sympathetic activation of lipid synthesis in brown adipose tissue in the rat.

1. The roles of the sympathetic nerves in regulating lipid synthesis in brown adipose tissue (BAT) were studied by measuring incorporation of 3H from 3H2O into glyceride glycerol and glyceride fatty acids in the interscapular BAT in anaesthetized rats. 2. When noradrenaline was infused intravenously at a total dose of 1-8 micrograms/100 g body weight over 30 min, 3H incorporation into glyceride glycerol increased whereas 3H incorporation into fatty acids did not change. Similar responses were found when the sympathetic nerves entering the interscapular BAT were stimulated continuously at 10 Hz. However, when electrical stimuli consisting of a much shorter train (2 s) were applied to the nerves at 3 min intervals at 10 Hz (stimulation in bursts). 3H incorporation into both glyceride glycerol and fatty acids was enhanced. Stimulation in bursts elicited more pronounced lipogenic responses than other patterns that were employed, and involved the delivery of precisely the same number of impulses over the whole period of stimulation. The lipogenic responses to nerve stimulation in bursts were increased by increasing the stimulus frequency over the range 4-40 Hz. 3. Simultaneous administration of propranolol and phenoxybenzamine had little effect on either the fatty acid or the glyceride glycerol response to nerve stimulation. In contrast, these blocking agents almost completely eliminated the responses to noradrenaline infusion. 4. Pre-treatment with guanethidine effectively abolished the lipogenic response to nerve stimulation but potentiated the response to noradrenaline infusion. 5. It is concluded that lipid synthesis in BAT is enhanced by direct electrical stimulation of the sympathetic nerves only when they are stimulated in bursts. Sympathetic activation of lipogenesis in BAT is not solely attributable to the action of noradrenaline but involves some non-adrenergic mechanism.

Adipose Tissue↗
PubMed2004

Brown adipose tissue glyceroneogenesis is activated in rats exposed to cold.

We have previously found that glyceroneogenesis is very active in brown adipose tissue (BAT) and increases in fasted, diabetic and high-protein-diet-fed rats, situations of reduced thermogenic activity. To understand better the role of glyceroneogenesis in BAT glycerol-3-phosphate (G3P) generation, we investigated its activity during cold exposure (10 days at 4 degrees C), a condition in which, in contrast to the above situations, BAT thermogenesis is markedly activated. Rates of total (from all sources) BAT fatty acid (FA) synthesis and rates of incorporation of glucose carbon into BAT glyceride-FA and -glycerol in vivo were markedly increased by cold exposure. Cold exposure induced a marked increase in BAT glyceroneogenic activity, evidenced by (1) increased rates of non-glucose carbon incorporation into glyceride-glycerol in vivo and of [1-14C]-pyruvate incorporation into glyceride-glycerol in vitro, and (2) a threefold increase in phosphoenolpyruvate carboxykinase activity. Most of the glyceride-glycerol synthesized by BAT via glyceroneogenesis or from glucose was used to esterify preformed FA. This use was markedly increased by cold exposure, in parallel with a pronounced activation of BAT lipoprotein lipase activity. In conclusion, during cold exposure BAT glyceroneogenesis is markedly activated, contributing to increase the generation of G3P, which is mostly used to esterify preformed FA.

Adaptation, Physiological↗
PubMed2006

Molecular dynamics simulations to aid the rational design of organic friction modifiers.

Molecular dynamics simulations were performed under conditions of constant volume and temperature and of constant pressure and temperature to elucidate the structure activity relationships of a series of non-ionic surfactant molecules derived from vegetable fat and employed as friction modifiers in commercial engine oils. The simulations show the extent to which intermolecular hydrogen bonding is important in determining the stability of the monolayer formed by the surfactant molecules and show that mono-alkanoyl glyceride molecules are able to pack more efficiently, forming significantly more intermolecular hydrogen bonds and occupying approximately half the volume needed by di-alkanoyl glyceride molecules. Density profiles are presented which show significant mixing of the hydrophobic tail groups and a non-polar solvent. The distribution of torsion angles in the tail groups shows that the conformation is consistent with a liquid at finite temperature rather than a crystal structure. The measured friction coefficients of equimolar solutions of the glycerides show that the efficacy as friction modifiers varies in the order mono-, di- and the tri-oleyl glyceride, which is consistent with the efficacy of film formation predicted by the molecular dynamics calculations.

Computer Simulation↗
PubMed2000

Rationale and applications of lipids as prodrug carriers.

Lipidic prodrugs, also called drug-lipid conjugates, have the drug covalently bound to a lipid moiety, such as a fatty acid, a diglyceride or a phosphoglyceride. Drug-lipid conjugates have been prepared in order to take advantage of the metabolic pathways of lipid biochemistry, allowing organs to be targeted or delivery problems to be overcome. Endogenous proteins taking up fatty acids from the blood stream can be targeted to deliver the drug to the heart or liver. For glycerides, the major advantage is the modification of the pharmacokinetic behavior of the drug. In this case, one or two fatty acids of a triglyceride are replaced by a carboxylic drug. Lipid conjugates exhibit some physico-chemical and absorption characteristics similar to those of natural lipids. Non-steroidal, anti-inflammatory drugs such as acetylsalicylic acid, indomethacin, naproxen and ibuprofen were linked covalently to glycerides to reduce their ulcerogenicity. Mimicking the absorption process of dietary fats, lipid conjugates have also been used to target the lymphatic route (e.g., L-Dopa, melphalan, chlorambucil and GABA). Based on their lipophilicity and resemblance to lipids in biological membranes, lipid conjugates of phenytoin were prepared to increase intestinal absorption, whereas glycerides or modified glycerides of L-Dopa, glycine, GABA, thiorphan and N-benzyloxycarbonylglycine were designed to promote brain penetration. In phospholipid conjugates, antiviral and antineoplasic nucleosides were attached to the phosphate moiety. After presenting the biochemical pathways of lipids, the review discusses the advantages and drawbacks of lipidic prodrugs, keeping in mind the potential pharmacological activity of the fatty acid itself.

Animals↗
PubMed1972

Intracellular distribution of enzymes of the cytidine diphosphate choline pathway in castor bean endosperm.

The occurrence and subcellular distribution of enzymes of the cytidine diphosphate choline pathway of lecithin synthesis have been examined. Choline kinase (EC 2.7.1.32) was completely soluble, while phosphorylcholine-cytidyl transferase (EC 2.7.7.15) and phosphorylcholine-glyceride transferase (EC 2.7.8.2) were associated with particulate fractions. Although components sedimenting at 10,000 to 100,000 x g contained both enzymes, phosphorylcholine-cytidyl transferase and particularly phosphorylcholine-glyceride transferase were present in the 10,000 x g pellet, which contained the major organelles, mitochondria, and glyoxysomes. When the crude homogenate was centrifuged on a sucrose density gradient, four major bands of particulate protein were recovered. A band at density 1.24 g/cm(3) contained the glyoxysomes and was devoid of phosphorylcholine-cytidyl transferase and phosphorylcholine-glyceride transferase activity. Enzyme activity was barely detectable in the mitochondria, at density 1.18 g/cm(2). Phosphorylcholine-glyceride transferase was found almost exclusively in a sharp band at density 1.12 g/cm(3), and phosphorylcholinecytidyl transferase was found in the uppermost band at density 1.08 g/cm(3). Thus, for the synthesis of lecithin in their membranes, the glyoxysomes and mitochondria depend on enzymes elsewhere in the cell; the final two steps in lecithin formation occur, apparently exclusively, in separate particulate cell components.

Carbon Isotopes↗
PubMed1988

Glucose metabolism in isolated adipocytes from ad Libitum- and restricted-fed lean and obese Zucker rats at two different ages.

Chronic food restriction in Sprague-Dawley rats has been shown to alter adipose glucose metabolism. In the present study, lean and obese male Zucker rats were food restricted from 5 weeks until either 10 or 26 weeks of age and adipocyte glucose metabolism was measured. Adipocytes from restricted-fed lean and obese Zucker rats converted more glucose to CO2 and fatty acids than those from their ad libitum-fed counterparts in both the absence and the presence of increasing doses of insulin at 10 weeks of age. At the highest insulin dose, adipocytes from restricted-fed obese rats converted significantly more glucose to CO2 and fatty acids than did those from restricted-fed lean rats. Basal glyceride-glycerol values were similar in all groups at this age. At the 0.4 and 2.0 ng/ml insulin levels, glyceride-glycerol production was highest in restricted-fed lean rats; restricted-fed obese and ad libitum-fed lean rats had similar values; and ad libitum-fed obese rats had the lowest. At the 20 ng/ml dose, glyceride-glycerol values of restricted-fed rats were higher than those of ad libitum-fed rats. Basal and insulin-stimulated values were compared within each group. Most basal versus insulin-stimulated values were significantly different for the two lean groups. For ad libitum-fed obese rats, only 0 versus 20 ng/ml insulin values were significant. Restricted-fed obese rats had significant increases in 0 versus both 2 and 20 ng/ml insulin values. Restricted-fed obese rats had significantly lower serum insulin levels relative to ad libitum-fed obese rats at 10 weeks of age. Adipocytes from all rats at 26 weeks of age had similar basal rates of conversion of glucose metabolism to all three metabolites. In the presence of insulin, adipocytes from restricted-fed lean rats metabolized significantly more glucose to CO2 and glyceride-glycerol than adipocytes prepared from the three other groups. Fatty acid production was similar in all groups at each insulin level. Only restricted-fed lean rats showed consistent significant responses to insulin stimulation for the three metabolites. Whether these results are due to age, length of food restriction, or serum insulin levels remains to be determined.

Adipose Tissue↗
PubMed1990

Effects of prolactin and androgens on the prostatic lipids of castrated mature bonnet monkeys.

The effects of prolactin (PRL), bromocriptine (Br), testosterone propionate (TP), dihydrotestosterone (DHT), and the combinations of these androgens with PRL/Br on total lipid, total cholesterol, total glyceride glycerols, and total phospholipid and their fractions in cranial and caudal prostates of castrated mature monkeys were studied. Glyceride glycerols formed the major portion of total lipids (50%) in normal monkeys. Cholesterol and phospholipids were of equal share (25%). Esterified cholesterol formed the major share (75%) of total cholesterol. Diacyl glycerol was the major (60%) glyceride glycerol and phosphatidyl choline and ethanolamine were the major phospholipid classes. Except triacyl glycerol castration markedly decreased all the lipid classes in both the lobes. PRL restored normal free and esterified cholesterol and phosphatidyl inositol but Br invariably decreased all the lipid classes. TP/DHT treatment stimulated the free and esterified cholesterol more than the control; it restored the normal glyceride glycerols in both the lobes. Phosphatidyl inositol, choline, and ethanolamine were stimulated by androgens and other phospholipid classes were brought to normal in both the lobes. Addition of PRL + TP/DHT markedly increased esterified cholesterol, phosphatidyl inositol, choline, ethanolamine, and phosphatidic acid in both the lobes. Br counteracted the effects of androgens and prolactin. In general, the influence of prolactin was more in the caudal lobe than cranial. The results are discussed in detail with available literature.

Animals↗
PubMed1984

The effect of pyridoxal phosphate-induced convulsive seizures on rat brain phospholipid metabolism.

The intraventricular injection of pyridoxal phosphate (PLP; 1 mumole/brain) to rats causes convulsive seizures beginning 3 min after injection and lasting for about 20 min. The incorporation of [2-3H] glycerol into rat brain glycerides has been studied to ascertain whether treatment with PLP affects the incorporation of label into various lipid classes. The labeling pattern of glycerides is changed by the administration of PLP. The observed alterations begin a few min after injection, together with the convulsive seizures. 1 h after the injection the pattern of labeling of brain glycerides returns to normal. Different glycerides are differently affected by PLP. This work demonstrates that the labeling of diglyceride increases whereas that of phosphatidylethanolamine decreases following PLP administration.

Animals↗
PubMed1982

Rat adipocyte utilization of different substrates: effects of cell size and the control of lipogenesis.

The metabolism of labeled glucose, pyruvate and acetate was compared in adipocytes isolated from old, obese rats (greater than 500 g) and young, lean rats (130-150 g). The larger cells from old, obese rats had markedly reduced rates of glucose, pyruvate and acetate conversion to glyceride-fatty acids, indicating that large cell fatty acid formation is reduced at some point beyond the entry of pyruvate and acetate into glucose metabolism. No evidence of a primary block in the pentose phosphate cycle of cells from old, obese rats was found. In spite of diminished glucose metabolism to several products in the large cells, both basal and insulin-stimulated rates of glyceride-glycerol synthesis from glucose and pyruvate were similar in each cell type. This indicates a relative diversion of carbon flow to alpha-glycerophosphate and reesterification in the large cells. Addition of low concentrations of glucose increase glyceride-fatty acid synthesis from acetate (both cell types) or pyruvate carbon (small cells), but decreased glyceride-glycerol synthesis from pyruvate carbon (both cell types). The acceleration of small cell fatty acid synthesis from pyruvate carbon by glucose and insulin was shown to be related to provision of NADPH from glucose metabolism in the pentose cycle. These studies indicate that, although the block in lipogenesis in adipocytes from old, obese rats appears to reside in the pathway of fatty acid synthesis itself, provision of additional alpha-glycerophosphate or NADPH from glucose metabolism may, under certain conditions, increase lipogenesis in cells from old, obese and young, lean rats.

6-Aminonicotinamide↗
PubMed1975

Effect of PGE1 on gluconeogenesis and glycerol esterification in perfused liver of fasted rats.

Using perfused livers of rats fasted for 48 hours, glucose production and incoroporation of 2-14C pyruvate (trace dose) into perfusate glucose were studied. Both were found to be inhibited by PGE1 (infuced at a concentration of 0.5 mu/min) by about 60%. The incorporation of 1-14C glycerol into perfusate glucose and into glycerol-glyceride part of the liver glycerides were also studied, using the same test conditions. The former incorporation was significantly inhibited (56%) and the latter strongly stimulated (360 %) by PGE1. PGE1 had no effect on glucose production in a perfusate overloaded with sodium pyruvate, nor on pyruvate carboxylase and phospho-enolpyruvate carboxykinase activity. this was in contrast with the results obtained in perfusions with a trace dose of 2-14C pyruvate. The results showed that PGE1, at the physiological concentration used, stimulated the incorporation of 1-14C glycerol into glycerol-glyceride part of liver glycerides and, when there was no overload of pyruvate present in the perfusion medium, inhibited gluconeogensis at some point, possibly, but perhaps not exclusively, between the glycerol and glucose steps.

Animals↗
PubMed1975

Triglyceride-production rates in patients with type-4 hypertriglyceridaemia.

A new method has been devised to study triglyceride-production rates in man. The clearance of plasma-triglyceride transported on very-low-density lipoproteins (V.L.D.I.) to peripheral tissues is inhibited by about 50 percent with protamine sulphate; and this results in a rise of blood-glycerides over 1 hour. In a group of nine patients with type-IV hypertriglyceridaemia (mean fasting glycerides 252 mg. per 100 ml.) the mean increment of plasma-triglycerides was 29.8 compared with 1.4 mg. per 100 ml. per hour for nine controls whose mean fasting glycerides had been only 105 mg. per 100 ml. Patients with fasting plasma-triglycerides greater than 400 mg. per 100 ml. showed a response to protamine more like controls. It is suggested that patients with type-IV hyperlipaemia and fasting levels of triglycerides less than 400 mg. per 100 ml. are secreting triglycerides into blood at greater rates than controls; whereas patients with sever hypertriglyceridaemia (levels greater than 400 mg. per 100 ml.) may have a defect of triglyceride clearance so that inhibition by protamine produces no further change in level of plasma glycerides.

Adult↗
PubMed1983

The intake of milk by suckled, newborn lambs and the effects of twinning and cold exposure.

Clun Forest ewes with single and twin lambs were exposed to neutral (20 degrees) or cold (-1 degree) environmental temperatures, beginning soon after parturition, for 4 d. The intakes of milk, lactose and glycerides by the lambs were calculated from measurements of the rate of displacement of tritiated water (injected into the lambs) by non-radioactive water in milk from the ewes, and measurements of the concentration of lactose and glyceride glycerol in small samples of milk. The yield of milk from ewes bearing twin lambs was greater than the yield from single-bearing ewes in the neutral environment but, in both environments, twin lambs had lower intakes of milk and milk lactose and glycerides, and gained body-weight more slowly, than single lambs. Milk from twin-bearing ewes had a lower lactose concentration than milk from single-bearing ewes. Cold exposure reduced the intake of milk and milk lactose, and reduced the rate of weight gain, of single and twin lambs. Glyceride intake was not different in the two environments. There appears to be a conflict between reduced supply of milk by the ewe and increased demand for milk by the lamb in cold temperatures. Such a conflict is sharpened when twin lambs are born.

Animal Nutritional Physiological Phenomena↗
PubMed1993

Two Isoforms of Dihydroxyacetone Phosphate Reductase from the Chloroplasts of Dunaliella tertiolecta.

Three isoforms of dihydroxyacetone phosphate reductase in extracts from Dunaliella tertiolecta have been separated by a diethylaminoethyl cellulose column chromatography with a shallow NaCl gradient. The chloroplasts contained the two major isoforms, and the third, minor form was in the cytosol. The isoforms are unstable in the absence of glycerol and they are cold labile, but they may be partially reactivated at 35[deg]C. The first chloroplast form to elute from the DEAE cellulose column was the major form when the cells were grown on high NaCl and it has been referred to as the form for glycerol production for osmoregulation or "osmoregulator form." The second form increased in specific activity when inorganic phosphate was increased in the growth media to stimulate growth, and it has been given the designation for the form for glyceride synthesis, "glyceride form." The osmoregulator form was stimulated by NaCl added to the enzyme assay, but not by reduced Escherichia coli thioredoxin. The glyceride form had properties similar to the enzyme in leaf chloroplast, such as inhibition by NaCl and by fatty acyl-coenzyme A derivatives and some stimulation by dithiothreitol, uridine diphosphate galactose, cyti-dine diphosphate dipalmatoyl diglyceride, and reduced E. coli thioredoxin. Thus, Dunaliella chloroplasts have a salt-stimulated osmoregulatory form of dihydroxyacetone phosphate reductase, which seems to have a role in glycerol production, and an isoform, which may be involved in glyceride synthesis and which has properties similar to the enzyme in chloroplasts of higher plants.

Journal Article↗