Rate Of Lipid Synthesis Research Articles

Methanogenesis and microbial lipid synthesis in anoxic salt marsh sediments

In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments, the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.

Altered interactions between glycogenesis and lipid synthesis after liver resection: specific effects of liver regeneration, coupled with non-specific effects of surgery.

1. This work investigated the relationship between glycogenesis and lipid synthesis during liver regeneration after partial hepatectomy in the rat. 2. Rates of lipid synthesis were increased during the first 2 post-operative days; these elevated rates were unaffected by starvation. By contrast, glycogen concentration were decreased even after 8 post-operative days, by which time liver mass had been restored and concentrations were sensitive to nutritional status. 3. The results of experiments involving the intragastric or intraperitoneal administration of glucose indicated that increased lipid synthesis was unlikely to be a consequence of decreased glycogenesis, but that depletion of liver glycogen might be linked both to liver cell division and, in the longer term, surgical stress.

Regulation of Bovine Adipose Tissue Metabolism During Lactation. 5. Relationships of Lipid Synthesis and Lipolysis with Energy Intake and Utilization1,2

The effects of energy utilization during lactation on adipose tissue metabolism were determined in 51 first lactation Holstein heifers producing between 5950 and 10,246kg milk in 305 d. Net energy intake ranged from 18.3 to 40.6 Mcal/d during 28 to 140 d of lactation. Milk yield ranged from 13.5 to 47.4 kg/d and fat percent from 1.49 to 4.60 during 28 to 140 d, providing a range of 8.2 to 32.6 Mcal/d milk energy secretion. Calculated energy balance ranged from −16.4 to 11.5 Mcal/d. Weight change ranged from −70 to 143kg during that 112-d period. Subcutaneous adipose tissue was biopsied nine times from 30 d prepartum to 15 d after lactation ceased. Adipose lipid synthesis measured prepartum was negatively related to subsequent milk energy secretion. Net energy intake, body weight, and body weight change were related positively to adipose lipid synthesis rates from 28 to 56 d, but those rates were related negatively to milk energy secretion. Lipolysis was positively related to milk energy secretion and body weight and negatively related to NE intake. At d 60 of lactation, adipose tissue lipid synthesis rates were a function of body weight, weight gain, and net energy intake. However, catecholamine-stimulated lipolysis rates were a function of body weight and milk energy secretion. After 140 d, lipid synthesis and lipolysis were elevated and more closely related to the previous peak rather than to concomitant milk energy secretion. These relationships demonstrate the effects of dietary energy content and genetic selection for milk production on adipose tissue metabolism.

Comparison of the flux of carbon to hepatic glycogen deposition and fatty acid and cholesterol synthesis on refeeding rats fed ad libitum or meal-fed rats with a chow-diet meal.

Meal-fed rats and rats fed ad libitum had similar rates of hepatic glycogen deposition on refeeding with a chow meal. In contrast, the rate of hepatic lipid synthesis (cholesterol plus fatty acids) was 6-fold higher on refeeding in the meal-fed group compared with the 'ad libitum' group. There were no significant differences in the gastrointestinal or hepatic contents of glucose or lactate between the two groups. It is suggested that in the meal-fed group exogenous glucose may be directly converted into glycogen, whereas the substrate for lipid synthesis is a C3 unit.

Photosynthetic Carbon Metabolism by Phytoplankton in a Nitrogen-Limited Reservoir

Phytoplankton in the downlake epilimnion of Normandy Lake, a central Tennessee reservoir, responded to summer N deficiency by increasing relative rates of lipid synthesis from 10–15% up to 20–35% of the total photosynthetic C fixation. Phytoplankton in more N-sufficient areas of the reservoir (downlake in a metalimnetic chlorophyll peak and uplake near the river inflow) maintained lower rates of lipid synthesis, generally [Formula: see text] of the total fixed C, throughout the summer. NH4 enrichment of N-deficient phytoplankton inhibited photosynthesis and significantly depressed the high lipid synthesis rates; however, NH4 enrichment had no effect on the phytosynthesis or lipid synthesis of N-sufficient phytoplankton. Our results document, for the first time, the occurrence of high lipid synthesis rates associated with the N limitation of natural phytoplankton assemblages. This relationship has previously been observed only in laboratory algal culture studies.

Lipid synthesis and deposition by adult Richardson's ground squirrels in the natural environment.

Adult male Richardson's ground squirrels, Spermophilus richardsonii, were estimated to have emerged from hibernation in late February to early March, and adult females in mid to late March. Half of the females trapped in late March were not pregnant, as against 10% after that time. In late March males and all females had similar WAT (white adipose tissue) deposits. Between late March and early June, WAT deposits in males increased from 14 g to 64 g (a rate of 5.6 g per week). In non-parous females WAT deposits increased from 13 g to 48 g from late March to late May (4.2 g per week). Fat deposits decreased during lactation but thereafter increased from 8 g to 29 g (a rate of 6.0 g per week) between early May and early June. In males the rate of fatty acid synthesis in BAT (brown adipose tissue), liver and WAT did not change from late March to late May, and rates in the corresponding tissues of non-pregnant females were similar to those in males. Fatty acid synthesis decreased during late pregnancy and lactation. After lactation, the rate of fatty acid synthesis in all tissues increased to that in males and non-pregnant females. Males initiated fattening 5-7 weeks earlier than females. It is concluded that compared with adult males, the later immergence of adult female Richardson's ground squirrels into hibernation is due primarily to later initiation of fattening and less to differences in rate of lipid synthesis after the reproductive period. Rates of fatty acid synthesis in liver and BAT were several times greater than that in WAT. The former tissues may contribute fatty acids for prehibernatory fattening.

The inhibition of lipid synthesis in vitro in the locust, Schistocerca gregaria, by factors from the corpora cardiaca

ABSTRACT. The rate of lipid synthesis from [14C]acetate in fat body from Schistocerca americana gregaria has been studied in vitro. Maximum incorporation is found on days 6–10 in adults and day 4 of the fifth stadium. The label appeared in the fatty acid components of triacyl‐glycerol, diacylglycerol and phospholipid.Lipid synthesis in vitro was inhibited by extracts of corpora cardiaca, and such inhibition was most marked (up to 85%) in fat bodies from insects at stages where fatty acid synthesis was greatest. HPLC separation of corpora cardiaca extracts gave several active fractions of which the most active was adipokinetic hormone 1 (AKH‐1).

The capacity of plastids from developing pea cotyledons to synthesise acetyl CoA

In order to determine whether the enzymes required to convert triose phosphate to acetyl CoA were present in pea (Pisum sativum L.) seed plastids, a rapid, mechanical technique was used to isolate plastids from developing cotyledons. The plastids were intact and the extraplastidial contamination was low. The following glycolytic enzymes, though predominantly cytosolic, were found to be present in plastids: glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.12), phosphoglycerate kinase (EC 2.7.2.3), and pyruvate kinase(EC 2.7.1.40). Evidence is presented which indicates that plastids also contained low activities of enolase (EC 4.2.1.11) and phosphoglycerate mutase (EC 2.7.5.3). Pyruvate dehydrogenase, although predominantly mitochondrial, was also present in plastids. The plastidial activities of the above enzymes were high enough to account for the rate of lipid synthesis observed in vivo.

Regulation of lipid synthesis in relation to keratinocyte differentiation capacity

Cultured keratinocytes and squamous carcinoma cells provide a useful model system for studying the processes involved in the regulation of differentiation, as the differentiation capacity of the cells can be modulated experimentally by changing the extracellular calcium concentration. Furthermore, the squamous carcinoma cell lines exhibit a defect in their differentiation capacity which they express to different extents. In this paper, the effect of external lipoproteins has been studied on lipid synthesis in normal keratinocytes and three squamous carcinoma cell (SCC) lines which showed a decreasing capacity to differentiate in the order of normal keratinocytes > SCC-12F2 > SCC-15 > SCC-4. The ability of the cells to form comified envelopes was taken as a measure of differentiation capacity. The rate of total lipid synthesis as well as the phospholipid-neutral lipid ratio decreased in the order SCC-4 > SCC-15 > SCC-12F2 ⩾ normal keratinocytes, clearly correlating with the differentiation capacity of the cells. Because of the high rate of phospholipid synthesis and the low rate of ceramide synthesis, it is concluded that, under these in vitro conditions used, the maturation of keratinocytes proceeds to a lesser extent than that seen under in vivo conditions. In proliferating cells, in which the low-density lipoprotein (LDL) receptor is operative to a high extent, the rate of lipogenesis, especially that of neutral lipids, responded dramatically to changes of extracellular lipoprotein concentration. In the presence of lipoproteins a marked decrease of cholesterol and triacylglycerol synthesis and an increase of cholesterol ester synthesis has been observed. On the other hand, in differentiating cells lipogenesis appeared to be independent of extracellular lipoproteins, due to the absence of the LDL uptake mechanism, the only exception being the synthesis of triacylglycerols, the rate of which could be modulated to a certain extent by extracellular lipoproteins. The results presented here demonstrate a close inverse relationship between the regulation of lipogenesis by extracellular lipoproteins and the ability of the cells to differentiate.

Lipid synthesis in callus and protoplasts during culture: Analysis of dividing protoplasts of Petunia hybrida and non‐dividing protoplasts of Parthenocissus tricuspidata

The purpose of the investigation was to study the process, by which protoplasts derived from callus tissue overcome the hydrolysis of membrane phospholipids, which is induced by the isolation. Dividing protoplasts from Petunia hybrida L. (line SFla) and non‐dividing protoplasts from Parthenocissus tricurpidara L. crown gall (Morel strain) were fed with sodium [1‐14C]‐acetate for 1 h. The incorporation was carried out at protoplast isolation and after 1, 2, 4 and 7 days of culture. The rates of fatty acid and lipid synthesis were then followed. Isolation stress induced diversions in the utilization of the precursor via triacylglycerol (Petuunia) or diacylglycerol (Partheno‐cissus) and a decrease in the synthesis of oleic acid (Parrhenocissus). During the first 2 days of culture, the rate of phospholipid synthesis was similar in both systems. Later on, an increase in the rate and in the efficiency of phospholipid synthesis was observed in dividing Petunia protoplasts. The accelerated rate of lipid synthesis allowed them to recover the same partitioning and content in membrane phospholipids as the reference cells in the callus. This process seemed to bc related to cell division, since it was not observed in the non‐dividing protoplasts of Parthenocissus.

The effect of 3-methylindole on the rates of phospholipid and neutral lipid synthesis in cultured fibroblasts.

The present study was designed to test the hypothesis that a pneumotoxin, 3-methylindole, alters the basic metabolic pathways involved in phospholipid and neutral lipid synthesis in cultured fibroblasts. Rat skin fibroblasts were obtained from day-old pups. Confluent monolayers were preincubated for up to 24 h with a range of concentrations (0-0.76 mM) of 3-methylindole. Following these treatments, the cell lipids were labelled by incubation for 6 h with [14C]glycerol. The lipids were extracted, separated by thin layer chromatography, and the radioactivity in each fraction was determined. 3-Methylindole had no effect on the total incorporation of [14C]glycerol into lipids, but significantly altered the distribution among lipid fractions. Incubation with 3-methylindole caused a decrease in the incorporation of [14C]glycerol into phosphatidylcholine, while radioactivity accumulated in the neutral lipid fraction. The other lipid fractions responded variably. Similarily, Flow 2000 human diploid lung fibroblasts were incubated for 24 h with 3-methylindole followed by treatment with [14C]glycerol, resulting in a 74% decrease in the incorporation of [14C]glycerol into phosphatidylcholine and a 50% increase in its accumulation in neutral lipid. The results indicate that 3-methylindole inhibits the synthesis of phosphatidylcholine from diacylglycerol precursors on the endoplasmic reticulum in cultured fibroblasts. This is an important observation as it shows that 3-methylindole affects the synthesis of phospholipids required for membrane turnover in cells that are not specialized for the production of phospholipids for surfactant.

SILICATE DEFICIENCY AND LIPID SYNTHESIS OF MARINE DIATOMS1,2

ABSTRACTLipid synthesis of three marine diatoms was studied with a 14CO2 incorporation technique in silicate limited batch cultures. Growth rates were independent of the silicate concentration but the cellular yields were proportional to the initial amount of silicate. At the beginning of the stationary growth phase, lipid synthesis rates per unit culture volume increased by 1.7 times for Chaetoceros gracilis, 3.1 times for Hantzschia sp., and 2.8 times for Cyclotella sp., respectively compared to those during the exponential growth phase. Lipid carbon accounted for as much as 57% of the carbon in C. gracilis, 71% in Hantzschia sp., and 65% in Cyclotella sp., respectively. Additional enrichment with silicate during stationary growth phase allowed the cultures to grow further. Lipid synthesis rates were reduced during the subsequent growth phase, and the growth rates themselves were dependent on the level of biomass achieved during the previous stationary phase. However, the cellular yields were similar and probably controlled by light.

Properties of the enzymes catalyzing the biosynthesis of lysophosphatidate and its ether analog in cultured fibroblasts from Zellweger syndrome patients and normal controls

The activities, properties, and steady-state kinetics of the five enzymes catalyzing the synthesis of 1-acyl- and 1-alkyl- sn-glycerol 3-phosphate in the cultured skin fibroblasts from Zellweger syndrome patients and normal controls were studied in detail. Judging from their K m and V max values, glycerol phosphate acyltransferase (EC 2.3.1.15), acyl/ alkyl dihydroxyacetone phosphate reductase (EC 1.1.1.101), and acyl coenzyme A reductase (long-chain alcohol forming), appear to be affected only slightly by the absence of peroxisomes characteristic of the Zellweger syndrome. Glycerophosphate acyltransferase also showed no differences in N-ethylmaleimide sensitivity nor in inhibition by dihydroxyacetone phosphate between these cell types. Dihydroxyacetone phosphate acyltransferase (EC 2.3.1.42) and alkyl dihydroxyacetone phosphate synthase (EC 2.5.1.26) have altered activity and kinetic constants in homogenates from Zellweger syndrome fibroblasts. Dihydroxyacetone phosphate acyltransferase has similar K m (DHAP) values in both control and Zellweger syndrome cells; however, the value for the V max in Zellweger syndrome cells is only 6% of that found in the controls. This is interpreted as indicating that this enzyme is not defective in this disease but is simply present at a depressed level. Also, this enzyme activity has a maximum rate at pH 7.0–7.5 in the mutant cells as opposed to pH 5.4 in the controls. Acylation of dihydroxyacetone phosphate by control cell homogenate was stimulated by N-ethylmaleimide at both pH 5.7 and 7.5 whereas this activity from Zellweger syndrome cells was slightly inhibited at pH 5.7 and strongly inhibited at pH 7.5. In the absence of detergent, dihydroxyacetone phosphate acyltransferase in the Zellweger syndrome cells was much more labile to trypsin than in the control cells. Alkyl dihydroxyacetone phosphate synthase had a slightly higher K m (33 vs 17 μ m) for palmitoyl dihydroxyacetone phosphate and a lower V max (0.07 vs 0.24 mU/mg protein) in the Zellweger syndrome cells as compared to controls. Although this is a substantial decrease in activity, it probably contributes little to the decreased rate of ether lipid synthesis in these cells. The major problem in this respect is apparently the loss of dihydroxyacetone phosphate acyltransferase activity. All of these enzymes, in both control and Zellweger syndrome cell homogenates, are sedimentable by centrifugation at 100,000 g. Also, with the exception of dihydroxyacetone phosphate acyltransferase they had similar patterns of inactivation by heat in both cell types.

Ontogeny of Glucose Metabolism in Sympathetic Ganglia of Chickens. Concurrence of Maximum Rates in the Hexosemonophosphate Shunt and in Synthesis of Lipids but Not of Ribonucleic Acid

Chains of sympathetic ganglia were excised from the lumbar region of white Leghorn chicken embryos, 8-19 days of age, and incubated, usually for 5 h, at 36 degrees C in a bicarbonate-buffered physiological salt solution containing [U-14C]glucose, [1-14C]glucose, [6-14C]glucose, or [5-3H]uridine. Lipid synthesis was measured by the incorporation of 14C into lipids, and RNA synthesis by the accumulation of 3H into macromolecules. The ratio of 14C put out in CO2 during the second hour of incubation in the presence of [1-14C]glucose to that with [6-14C]glucose was used as an index of activity in the hexosemonophosphate shunt (HMS). Both the rate of lipid synthesis and activity in the HMS reached well-defined maxima at about 11 days of embryonic age. There was no evidence of a similar rise and fall of RNA synthesis during the ages studied. Estimates of the rate of NADPH production by the HMS at near-peak lipid synthesis varied over a twofold range that included the rate needed for the observed lipid synthesis. The results thus support, quantitatively as well as qualitatively, the supposition that the HMS is accelerated during development to sustain lipid synthesis.

The role of prolactin and progesterone in the regulation of lipogenesis in maternal and foetal rat liver in vivo and in isolated hepatocytes during the last day of gestation.

The administration of progesterone on day 21 of gestation increases the rates of lipogenesis in the liver in vivo and in hepatocytes isolated from rats on day 22 of pregnancy. Bromocriptine administration increases the rates of hepatic lipogenesis in vivo, but has no effect on lipid synthesis in hepatocytes under the same treatment conditions. Concurrently, the administration of progesterone or bromocriptine on day 21 to the mother increases the rates of lipogenesis in the foetal liver in vivo on day 22. The rates of lipid synthesis in foetal isolated hepatocytes are increased by progesterone administration, but remain unchanged by bromocriptine.

Cycloheximide sensitivity in regulation of acyl coenzyme A:cholesterol acyltransferase activity in Chinese hamster ovary cells. 2. Effect of sterol endogenously synthesized.

We reported in another paper [Chang, C. C. Y., Doolittle, G. M., & Chang, T. Y. (1986) Biochemistry (preceding paper in this issue)] that in Chinese hamster ovary (CHO) cells activation of acyl coenzyme A:cholesterol acyltransferase (ACAT) activity by treating cells with cycloheximide was abolished by providing exogenous sterol in the medium. We now report that providing 20 mM DL-mevalonate to cells grown in sterol-free medium increases the ACAT activity by approximately 6-fold and diminishes the cycloheximide activation effect. The mevalonate supplement has no significant effect on the rate of triglyceride or polar lipid synthesis, [3H]cholesterol efflux, or bulk protein degradation in cells. The activation of ACAT by mevalonate is prevented by adding a specific squalene oxide cyclase inhibitor to cells, indicating the requirement for endogenous sterol synthesis to mediate the mevalonate effect. In sterol-free medium, if sterol synthesis is blocked by specific enzyme inhibitors or through mutation, the ACAT activation by cycloheximide is again abolished. These results support the hypothesis that there may exist a short-lived factor(s) serving directly or indirectly as an endogenous ACAT inhibitor(s), the inhibitory action of this (these) factor(s) is (are) abolished, and its (their) turnover rate(s) is (are) increased by either exogenous sterol or by sterol endogenously synthesized. Conversely, removing exogenous sterol coupled with blocking endogenous sterol synthesis decreases the turnover rate(s) of the inhibitor(s), rendering its (their) action insensitive to intracellular degradation over the time period studied.

Cycloheximide sensitivity in regulation of acyl coenzyme A:cholesterol acyltransferase activity in Chinese hamster ovary cells. 1. Effect of exogenous sterols.

Chinese hamster ovary cells grown in medium containing low-density lipoprotein (LDL) express high acyl coenzyme A:cholesterol acyltransferase (ACAT) activity as measured by an [3H]oleate pulse. Removal of LDL from the medium causes rapid inactivation of ACAT activity; the t1/2 for the initial inactivation rate is 0.8 h. Preincubation with protein synthesis inhibitors (cycloheximide or emetine) for 2 h or longer lengthens the t1/2 for the initial inactivation rate to approximately 2.1 h. When LDL is removed for more than 10 h, the cells contain only 3% of the original ACAT activity. Cycloheximide under this condition causes an 8-fold increase in ACAT activity; the increase approaches a maximum in 6-8 h. The extent of ACAT activation by cycloheximide inversely depends on exogenous sterol present in the medium; LDL diminishes the activation, while cationized LDL or 25-hydroxycholesterol completely abolishes the activation. Adding LDL back to the sterol-free medium causes a 40-70-fold increase in ACAT activity; however, the activation of LDL is not further augmented if the cells are pretreated with cycloheximide. The above observations are qualitatively confirmed by ACAT assays in vitro with cell homogenates. LDL or cycloheximide has no effect on the rates of 3H-labeled triglyceride and 3H-labeled polar lipid synthesis. Efflux of prelabeled cholesterol from cells is cycloheximide-insensitive. Rates of degradation of [3H]-leucine-pulse-labeled total protein in cells grown with or without LDL are identical. The above results imply the existence of at least one specific short-lived factor that directly or indirectly inhibits ACAT activity.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Lipids in cells of atherosclerotic and uninvolved human aorta: II. Lipid metabolism in primary culture

[ 3H]Acetate and [ 3H]oleate were used to evaluate the rate of lipid synthesis in smooth muscle cells of human aorta. Experiments were carried out in primary cultures derived from the intima and media of unaffected and atherosclerotic vascular segments. The obtained results indicate that the rate of lipid synthesis in cells cultured from fatty streaks, atherosclerotic plaques, and underlying media is higher than in cells cultured from an uninvolved intima and media, respectively. The highest level of the label incorporation was observed in the fraction of phospholipids. In cultures obtained from fatty streaks and plaques, an increased incorporation of the labeled precursors into phospholipids, triglycerides, free sterols, and sterol esters was registered. The highest relative increase occurred in the fraction of sterol esters, the rate of acetate inclusion being five- to sixfold higher compared to the cell cultures derived from unaffected aortic segments. A direct and very close correlation was found between the rate of lipid synthesis and lipid levels in cells of normal and atherosclerotic aorta. The role of intracellular lipid metabolism disorders in the accumulation of excessive fat by “atherosclerotic” cells is discussed in this report.

Rapid effects of phorbol esters on isolated rat adipocytes. Relationship to the action of protein kinase C.

Treatment of isolated rat adipocytes with tumor-promoting phorbol esters, caused a fivefold stimulation of glucose oxidation, determined as 14CO2 production from [1-14C]glucose and a fivefold increase in the rate of lipid synthesis from [14C]glucose. Treatment of the cells with 12-O-tetradecanoylphorbol 13-acetate increased the rate of 86Rb+ uptake into the cells. Also phospholipase C was able to stimulate the rate of glucose oxidation; phospholipase C and 12-O-tetradecanoylphorbol 13-acetate stimulated glucose oxidation in a non-synergistic fashion, indicating a common mechanism for their action. Active phorbol esters and, in part, also phospholipase C, caused a translocation of protein kinase C activity from the soluble to the particulate fraction of the adipocytes. This process was rapid, being complete 30 s after the addition of phorbol ester, and resulted in the appearance of the kinase mainly in the mitochondrial and plasma membrane fractions. A comparison between the binding characteristics of adipocyte protein kinase C and the metabolic effects of the phorbol esters on the adipocytes revealed that the dose-response relationship did not correlate with binding of the phorbol esters, but, rather, a correlation was observed between the dose of phorbol esters required for translocation of protein kinase C and the intracellular effects. The results indicate that the intracellular translocation of protein kinase C might be a trigger for the effects of phorbol esters on the adipocyte and that binding of the esters to protein kinase C is not a sufficient event to cause this effect. Furthermore, it is suggested that activation of protein kinase C might be partly the action of hormones, such as insulin, on the fat cells.