palmitoyl-CoA Synthetase Research Articles

Intracellular localization of palmitoyl-CoA hydrolase and palmitoyl-CoA synthetase in human blood platelets and liver.

The intracellular localization studies of human blood platelets by sucrose gradient and differential centrifugation, showed that palmitoyl-CoA hydrolase was mainly localized in the cytosol fraction. However, a localization also in the mitochondrial fraction seems possible as disruption of platelets by the French press and nitrogen decompression techniques resulted in mitochondrial damage. In human liver the palmitoyl-CoA hydrolase was localized in the mitochondrial and microsomal fractions. Palmitoyl-CoA synthetase was localized in the mitochondrial and microsomal fractions in both platelets and liver. The possible physiological implications of these differences, and the finding of a very high ratio of palmitoyl-CoA hydrolase/palmitoyl-CoA synthetase in platelets compared with liver, are discussed.

Familial carnitine deficiency: A fatal case and subclinical state in a sister

A 15-year-old girl with a large accumulation of lipid in the muscle fibers, was suffering from systemic carnitine deficiency. She died in acidosis. The blood carnitine level was normal. At necropsy, carnitine levels were low in skeletal muscles and heart, whilst a normal level was found in the liver. Carnitine palmitoyltransferase II and palmitoyl-CoA synthetase activities were increased, whereas carnitine acetyltransferase, glycerol-3-phosphate dehydrogenase (FAD) and succinate dehydrogenase were decreased. Investigation of blood and skeletal muscle of the family members revealed marked abnormalities in a 7-year-old sister who had only minor neurological symptoms. Histochemical investigation revealed abnormal accumulations of lipid between the myofibrils. Carnitine was decreased in her skeletal muscle and blood. Muscular carnitine palmitoyltransferase II and palmitoyl-CoA synthetase were again increased in activity while glycerol-3-phosphate dehydrogenase (FAD) was decreased. The activities of succinate dehydrogenase, carnitine palmitoyltransferase I and glycerol-3-phosphate dehydrogenase (NAD +) were normal. The unexpected normal carnitine level in blood and liver of the deceased patient was attributed to muscle wasting, which was confirmed by the very high blood level of creatine phosphokinase. This fatal case indicates that the fasting condition must be avoided in persons with carnitine deficiency. In crises, glucose supply is necessary since gluconeogenesis may be blocked.

Purification and characterization of long-chain acyl-CoA hydrolase from rat liver mitochondria.

An enzyme able to hydrolyze long-chain acyl-CoA esters has been purified from mitochondrial matrix of rat liver by ammonium sulfate extraction, gel chromatography, and isoelectric focusing. The specific activity of the purified enzyme represented approx. 53-fold and 700-fold enrichment over the initial extract in the absence and presence of serum albumin, respectively. The enzyme has been purified to homogeneity as judged by polyacrylamide-gel electrophoresis in the absence and presence of sodium dodecyl sulfate. The enzyme has a sedimentation rate of 2.1 S in a sucrose gradient, a Stokes radius of 1.9 nm, and consists of a single polypeptide with a molecular weight of 19000 determined by gel chromatography. The isoelectric point (pI) of the enzyme is 6.0. The enzyme is specific for long-chain (over C10) fatty acyl-CoA esters with maximal activity for palmitoyl-CoA. At physiological substrate concentrations the enzyme did not hydrolyze palmitoyl-l-carnitine, tripalmitoyl-glycerol, dipalmitoyl-phosphatidylcholine, or cholesterol-oleate. The enzyme did not possess any palmitoyl-CoA synthetase or carnitine palmitoyltransferase activity. The hydrolase activity was strongly influenced by the acyl-CoA/protein ratio as serum albumin increased the activity. As this effect was also seen at acyl-CoA concentrations under the critical micelle concentration it seems likely that serum albumin not only prevents the inhibition of the enzyme by binding the inhibiting micellar form of the substrate, but also stabilizes the enzyme. Similar effects were found with the nonionic detergent, Triton X-100.

Fatty liver in hypervitaminosis A: synthesis and release of hepatic triglycerides.

Feeding large doses (30,000 IU/100 g body wt per day) of vitamin A to young rats for 2 days produced fatty liver, caused a stimulation of oxidation and esterification of [1-14C]palmitate by liver slices, and increased the activity of hepatic palmitoyl-CoA synthetase. Under similar conditions, however, release of hepatic triglycerides into the plasma, as judged from the post-Triton triglyceridemia, remained unaffected. It is indicated by the present findings that excessive intake of vitamin A produces fatty liver by stimulating the synthesis of triglycerides in liver without affecting the rate of secretion of hepatic triglycerides. An involvement of altered oxidation of fatty acids in the liver can also be ruled out because in hypervitaminosis A this process is increased rather than decreased as required for fatty liver production.

Specific requirement of lysophosphatidylcholine for palmitoyl-CoA synthetase of chicken intestine

The presence of palmitoyl-CoA synthetase (EC 6.2.1.3) in the brush borderfree particulate fraction of chicken intestinal mucosa is demonstrated. The enzyme was dependent on the simultaneous presence of lysophosphatidylcholine and Triton X-100 as well as ATP, CoA and Mg 2+ for maximal activity. Lysophosphatidylcholine could not be replaced by other lipids. Enzyme preparations solubilized by Triton X-100 or lysophosphatidylcholine were still dependent on the presence of detergents for maximal activity.

Biochemistry of development in insects. Triacyglycerol and phosphoglyceride biosynthesis by subcellular fractions.

1. A different biochemical behaviour has been previously shown during several stages of the development of the insect Ceratitis capitata; thus, the acyl transferase activity has a different participation in the pathways of synthesis of triacylglycerols and phosphoglycerides by either larval or pharate adult stages of development. The results reported here are concerned with the behavior of mitochondria and microsomes from larvae and pharate adults for the synthesis of triacylglycerols and phosphoglycerides. In all preparations of either mitochondrial or microsomal fractions the optimum protein amount, previously determined, has been used. 2. The highest incorporation of [14C]palmitate into triacylglycerols and phosphoglycerides was achieved by the microsomal fraction from the larval stage of development of the insect. However, mitochondrial fractions from pharate adults utilized higher levels of [14C]palmitate than the microsomal preparation. These differences were not correlated with the palmitoyl-CoA synthetase activity. 3. Glycerol 3-phosphate influenced the fatty acid incorporation in a different manner depending on the stage of development of the insect. Increasing concentrations of glycerol 3-phosphate stimulated the synthesis of triacylglycerols by microsomal and mitochondrial preparations. This effect was not exhibited by the subcellular preparations of pharate adults. 4. Double-label experiments using [14C]glycerol 3-phosphate and[3H]palmitate showed qualitative differences in the synthesis of triacylglycerols by mitochondrial preparations from either larvae of pharate adults. Incorporation of the labelled fatty acids to endogenous triglycerides was preferentially shown by the mitochondria larval preparations. The pathways of synthesis of triacylglycerols and phosphoglycerides by microsomal preparations showed only quantitative differences depending on the stage of development of the insect. 5. Acylation of 14C-labelled lyso-phosphatidylcholine and 14C-labelled lyso-phosphatidylethanolamine by [3H]olate was assayed in the presence of miochondrial and microsomal preparations from the different stages of development of the insect. Microsomal fractions showed an efficient acyl transferase activity mainly when lyso-phosphatidyl-ethanolamine was used as a substrate.

Topographic distribution of enzymes involved in glycerolipid synthesis in rat small intestinal epithelium

1. 1. The enzymes involved in glycerolphosphate and monoacylglycerol acylation of rat small intestine were more active in villi than in crypts. Monoglyceride acyltransferase (EC 2.3.1.22) was found to be absent from crypts. 2. 2. In the villi, the enzymes are mainly localized in microsomes, although low activities of palmitoyl-CoA synthetase (EC 6.2.1.3), glycerolphosphate acyltransferase (EC 2.3.1.15) and cholinephosphotransferase (EC 2.7.8.2) are found in mitochondria. Mitochondria lack monoglyceride acyltransferase and lysolecithin acyltransferase (EC 2.3.1.23), both of which are involved in the reacylation of alimentary partial glycerides. Therefore, this process is confined to microsomes. 3. 3. The monoacylglycerol and lysolecithin acyltransferases, as well as cholinephosphotransferase, are probably localized within the endoplasmic reticulum, since these enzymes are relatively Nagerse resistant (subtilisin; EC 3.4.2.1, compared with palmitoyl-CoA synthetase and glycerolphosphate acyltransferase, which are highly Nagarse-sensitive and therefore probably localized on the outside of the microsomes (and mitochondria). 4. 4. The physical separation of alimentary product reacylation from de novo synthetic processes provides the basis of metabolic compartmentation observed by other workers. 5. 5. The use of sucrose instead of a salt medium for the isolation and homogenization of small intestinal epithelial cells allowed the separation of mitochondria and microsomes by differential centrifugation without mutual contamination. 6. 6. Phospholipids were found to stimulate glycerolphosphate acylation in vitro. 7. 7. The glycerolphosphate and monoacylglycerol acylation pathways are not competitive.

Cellular energy metabolism during fetal development: VI. Fatty acid oxidation by developing brain

We have investigated fatty acid oxidation and development profiles of palmitoyl-CoA synthetase and carnitine palmitoyltransferase in homogenates of developing rat brain. Palmitate showed a peak rate of oxidation between 10 days and the time of weaning, after which activity declined to adult levels. Acetate oxidation increased until Day 10, plateaued until Day 18 when it increased sharply and remained elevated through Day 25 before declining to the adult level. Leucine oxidation also showed a late peak as compared with palmitate. Palmitoyl-CoA synthetase activity was highest in late fetal development and in the newborn after which activity declined gradually to adult levels. Carnitine palmitoyltransferase activity peaked at 10–15 days of age similar to the profile obtained for long chain fatty acid oxidation. During the period of peak fatty acid oxidation, cytochrome oxidase activity increased twofold but the developmental increase in fatty acid oxidation and enzyme levels was much greater than the increase in mitochondrial number. These data suggest that during periods of high fat intake in the suckling rat the brain has an increased capacity for long chain fatty acid oxidation and that in addition to ketone bodies and leucine, fatty acids may be utilized as an alternative substrate in developing brain.

Enzymes of glycerolipid synthesis in small-intestinal mucosa of foetal and neonatal guinea pigs.

1. The activities of some enzymes of glycerolipid synthesis were measured in homogenates obtained from the intestinal scrapings of 62-66-day foetuses and 2- and 8-day-old guinea pigs. 2. The ratio of protein concentration/DNA concentration was significantly higher (P greater than 0.001) in homogenized tissue from the neonatal compared with the foetal guinea pigs. Enzyme activities were therefore expressed relative to both protein and to DNA. 3. The specific activities (relative to DNA) of palmitoyl-CoA synthetase, glycerol phosphate acyltransferase and phosphatidate phosphatase were higher in homogenized tissues from neonatal than in those from the foetal guinea pigs. These activities are probably involved more in cell proliferation than in the absorption and transport of triacylglycerol. Its activity was not significantly different in the foetal and neonatal guinea pigs when expressed relative to DNA but it was lower in the neonatal guinea pigs when expressed relative to protein. The entry of food into the intestine after birth is therefore not necessary for its activity.

Palmitate activation and esterification in microsomal fractions of rat liver.

Palmitoyl-CoA synthetase activity in the microsomal fraction of rat liver was measured directly by palmitoyl-CoA production, and indirectly by converting the palmitoyl-CoA into palmitoylcarnitine under optimum conditions. Even in the latter system, palmitoyl-CoA accumulated. The rate of palmitoyl-CoA hydrolysis and the inhibition of palmitoyl-CoA synthetase by palmitoyl-CoA were each estimated to be less than 10% of the maximum rate of palmitoyl-CoA production. The concentration of palmitoyl-CoA present in the assay systems used for measuring palmitate esterification to glycerol phosphate and the activity of palmitoyl-CoA synthetase by using the carnitine-linked determination were measured. These concentrations were not altered by the addition of glycerol phosphate, or of carnitine plus carnitine palmitoyltransferase. The relationship between the activity of palmitoyl-CoA synthetase and the rate of glycerolipid synthesis was investigated. The latter activity was measured by using palmitoyl-CoA generated from palmitate, palmitoyl--AMP or palmitoylcarnitine. It is concluded that, at optimum substrate concentrations, the activity of glycerol phosphate acyltransferase is rate-limiting in the synthesis of phosphatidate by rat liver microsomal fractions. The implications of these results in the measurement of palmitoyl-CoA synthetase and in the control of glycerolipid synthesis are discussed.

Comparison of the acylation of sn- glycerol 3- phosphate and membrane-bound lipid in the microsomal fraction from rabbit brain throughout maturation

1. 1. Age-related changes in the specific activity of palmitoyl-CoA synthetase, sn-glycerol 3-phosphate acyltransferase (EC 2.3.1.15) and the esterification of [ 3H] palmitate into endogenous lipid in the microsomal fraction from rabbit brain have been determined throughout development. 2. 2. The increased specific activity of sn-glycerol 3-phosphate acyltransferase at the onset of myelination (rising in parallel with other lipogenic enzymes) is consistent with a direct role of the acyltransferase in promoting the accumulation of cerebral lipid. In adult brain microsomes, although the specific activity was low, the total activity was only 20% lower than during active myelination. 3. 3. Palmitoyl-CoA, synthesized by the palmitoyl-CoA synthetase in the microsomal membrane, was the preferred substrate for the esterification of sn-glycerol 3-phosphate. There was no evidence for a pool of palmitoyl-CoA formed from palmitate. 4. 4. The esterification of [ 3H] palmitate into membrane-bound lipid remained high throughout development and may be part of an acyl-exchange cycle via lysophospholipids. [ 3H] palmitate was incorporated into both neutral lipids and phospholipids, while phosphatidic acid was the major product of sn-[1(3)- 3 H]-glycerol-3-phosphate esterification. 5. 5. The microsomal fraction contained a pool of unesterified fatty acid, which was activated and esterified into sn-glycerol 3-phosphate.

Effect of acetaldehyde on fatty acid oxidation and ketogenesis by hepatic mitochondria

Acetaldehyde inhibited the oxidation of fatty acids by rat liver mitochondria as assayed by oxygen consumption and CO 2 production. ADP-stimulated oxygen uptake was more sensitive to inhibition by acetaldehyde than was uncoupler-stimulated oxygen uptake, suggesting an effect of acetaldehyde on the electron transport-phosphorylation system. This conclusion is supported by the decrease in the respiratory control ratio, associated with fatty acid oxidation. Acetaldehyde depressed ketone body production as well as the content of acetyl CoA during palmitoyl-1-carnitine oxidation. Acetaldehyde was considerably more inhibitory toward fatty acid oxidation than was acetate. Therefore, the inhibition by acetaldehyde is not mediated by acetate, the direct product of acetaldehyde oxidation by the mitochondria. Oxygen uptake was depressed by acetaldehyde to a slightly, but consistently, greater extent in the absence of fluorocitrate, than in its presence. This suggests inhibition of oxygen consumption from β-oxidation to acetyl CoA and that which arises from citric acid cycle activity. The inhibition of fatty acid oxidation is not due to any effect on the activation or translocation of fatty acids into the mitochondria. The depression of the end products of fatty acid oxidation (CO 2, ketones, acetyl CoA) as well as the greater sensitivity of palmitate oxidation compared to acetate oxidation, suggests inhibition by acetaldehyde of β-oxidation, citric acid cycle activity, and the respiratory-phosphorylation chain. Neither the activities of palmitoyl CoA synthetase nor carnitine palmitoyltransferase appear to be rate limiting for fatty acid oxidation.

Acute and chronic effects of ethanol on intestinal lipid metabolism

To assess the effects of ethanol on intestinal lipid metabolism, fatty acid oxidation and triacylglycerol synthesis were measured in intestinal slices incubated with ethanol. Ethanol, when used in concentrations likely to be achieved in the upper jejunum after moderate drinking, inhibited both palmitate and acetate oxidation, CO 2 production and triacylglycerol synthesis, whereas it enhanced the esterification of fatty acid with ethanol. The concentrations required for the inhibitory effect were much higher than those needed to saturate enzyme systems known to participate in ethanol oxidation. In vivo administration of ethanol-containing diets produced persistent changes of the intestinal slices with respect to fatty acid oxidation and triacyl-glycerol synthesis. Acute intragastric administration of ethanol (3 g/kg) one hour prior to sacrifice, inhibited both processes in slices obtained from the jejunum, but not in those derived from the ileum. By contrast, chronic ethanol feeding increased the ability for fatty acid oxidation and triacylglycerol synthesis both in the jejunum and in the ileum. This stimulatory effect was associated with significant enhancement of palmitoyl-CoA synthetase activity, suggesting increased fatty acid activation. The inhibition by ethanol in high concentrations of intestinal fatty acid oxidation and triacylglycerol synthesis probably reflects epithelial cell damage; by contrast, prolonged administration of ethanol results in a persistent enhancement of lipid metabolism which may reflect the presence of a different cell population in the intestine.

Changes in the activities of de novo fatty acid synthesis and palmitoyl-CoA synthetase in relation to myelination in rabbit brain

1. 1. Age-related changes in the activities of fatty acid synthetase and palmitoyl-CoA synthetase (EC 6.2.1.3) have been determined in rabbit brain from the foetal stage through to maturity. 2. 2. Fatty acid synthetase was most active in the soluble fraction of brain homogenates at 5 days of age, prior to the active phase of myelination. Palmitic acid was the major fatty acid synthesised throughout development. 3. 3. Palmitoyl-CoA synthetase had a constant specific activity in the full homogenate, but in the microsomal fraction reached a maximum specific activity at 15–20 days of age. The specific activity was higher than in the mitochondrial fraction which declined from birth. Most of the palmitoyl-CoA synthetase activity was present in the fraction containing cell membranes plus nuclei. 4. 4. From a comparison of the total activities of the enzymes involved in the metabolism of fatty acids in the brain, de novo fatty acid synthesis may be rate limiting compared with the esterification of synthesised fatty acids, but not in the further transformations of the synthesised fatty acids.

Enzymes of phospholipid metabolism in the plasma membrane of Acanthamoeba castellanii

Phospholipase A, lyophospholipase, acyl CoA hydrolase, and palmitoyl CoA synthetase are present in the plasma membrane of Acanthamoeba castellanii. The first three of these enzymes also occur in other cell fractions but in concentrations too low for the activities in the plasma membrane fraction to be accounted for by contamination by any other cell fraction. Palmitoyl CoA synthetase is restricted almost entirely to the plasma membrane and microsomal fractions; the microsomal activity is too low for the plasma membrane activity to be due to contamination by microsomes. Acyl COA:lysolecithin acyltransferase is predominantly localized in the microsomal fraction, but the activity of the plasma membrane is probably too great to be accounted for by microsomal contamination. CDPcholine:1,2-diglyceride cholinephosphotransferase is restricted almost entirely to the microsomal fraction. Phospholipase C was not detected in any cell fraction or in the growth medium.

Biosynthesis of lipids in golgi complex and other subcellular fractions from rat liver

1. 1. Golgi complex, rough and smooth microsomes, plasma membranes, mitochondria and nuclei from rat liver were isolated and their purity assessed using specific marker enzymes. 2. 2. The various subcellular fractions were assayed for the following processes: biosynthesis of sphingomyelin, CDPdiglycerides, phosphatidylinositol, phosphatidylserine, the conversion of phosphatidylserine into phosphatidylethanolamine, the formation of lecithin via N-methylation, and the activation of palmitic and octanoic acids. 3. 3. None of these processes were found to be present in Golgi complex. 4. 4. The endoplasmic reticulum appears to be the principal site in the cell for the synthesis of sphingomyelin, CDPdiglycerides, phosphatidylinositol, phosphatidylserine and the formation of lecithin. Interestingly, the biosynthesis of phosphatidylserine appears to be four times more active in rough than in smooth microsomes, which might suggest a ribosomal localization of this process. 5. 5. Except for CDPdiglyceride synthesis, mitochondria do not contain any of the synthesizing activities described in 4. Mitochondria are, however, the only site in the cell where phosphatidylserine is decarboxylated. This activity appears to be localized in the inner membrane. 6. 6. The activation of palmitate is localized predominantly in endoplasmic reticulum and mitochondria, though some activity was detected in plasma membranes as well. All other cell organelles, including Golgi and probably nuclei, did not contain significant palmitoyl-CoA synthetase activity. The subcellular distribution of octanoyl-CoA synthetase resembled that of palmitoyl-CoA synthetase except that the former enzyme is more active in mitochondria than in microsomes.

Identification of the palmitoyl-CoA synthetase present in the inner membrane-matrix fraction of rat liver mitochondria

1. 1. The palmitoyl-CoA synthetase (palmitate: CoA ligase (AMP)) present in the inner membrane-matrix fraction of rat liver mitochondria was studied after the outer membrane acyl-CoA synthetase (acid:CoA ligase (AMP), EC 6.2.1.3) had been destroyed by the protease Nagarse. 2. 2. When Nagarse-treated liver mitochondria are subfractionated in a membraneous and a soluble fraction, both palmitoyl-CoA synthetase and octanoyl-CoA synthetase (acid: CoA ligase (AMP), EC 6.2.1.2) are distributed between these fractions as malate dehydrogenase. This indicates that both acyl-CoA synthetase activities are localized in the matrix mitochondrialis. 3. 3. When this mitochondrial soluble fraction is submitted to Sephadex G-100 chromatography, both palmitoyl-CoA synthetase and octanoyl-CoA synthetase activities reside in one single peak with a calculated molecular weight of 47000. For acetyl-CoA synthetase (acetate: CoA ligase (AMP), EC 6.2.1.1.), also present in this soluble fraction, a molecular weight of 62000 was calculated. 4. 4. Kinetic experiments performed with fractions purified by Sephadex chromatography clearly showed that palmitate is activated by the same enzyme as octanoate. This indicates that no special palmitoyl-CoA synthetase is present in the inner membrane-matrix fraction of rat liver mitochondria.

The separation and enzymatic characterization of inner and outer membranes of rat-heart mitochondria

1. 1. The procedure of Sottocasa, G. L., Kuylenstierna, B., Ernster, L. and Bergstrand, A. [(1967) J. Cell. Biol. 32, 415–438] for the separation of liver mitochondrial membranes was applied to rat-heart mitochondria. It appeared that the procedure did not result in a separation of the outer and inner membranes. It was found that the addition of a proteinase was essential to obtain the separation, suggesting that peptide bonds are involved in the binding between the inner and outer membrane. An optimal yield of outer membranes was obtained at 30–60 μg trypsin (EC 3.4.21.4) per mg mitochondrial protein. 2. 2. The contamination of the outer membrane fraction with inner membrane fragments was counteracted by the use of a high mitochondrial protein concentration. 3. 3. The outer membranes were 6-fold purified in a yield of up to 34%. They contained monoamine oxidase (EC 1.4.3.4), rotenone-insensitive NADH-cytochrome c reductase, palmitoyl-CoA synthetase (EC 6.2.1.3) and lauroyl-CoA synthetase. Creatine kinase (EC 2.7.3.2) remained bound to the inner membranes, while adenylate kinase (EC 2.7.4.3) was solubilized.

The activation and oxidation of octanoate and palmitate by rat skeletal muscle mitochondria

1. 1. Rat skeletal muscle mitochondria can oxidize octanoate just as well as palmitate. The oxidation of both fatty acids is strongly carnitine dependent, which indicates that the fatty acid CoA ester formation (fatty acid activation) is localized on the outer membrane. 2. 2. The palmitoyl-CoA synthetase and octanoyl-CoA synthetase activities were measured in these mitochondria. Palmitoyl-CoA synthetase was inhibited by octanoate while the octanoyl -CoA synthetase was inhibited by palmitate. Both inhibitions seem to be of the competitive type. These results suggest that both fatty acids are activated by the same enzyme. 3. 3. Octanoyl-CoA synthetase in rat skeletal muscle mitochondria was strongly (3 to 4 times) stimulated by the addition of skeletal muscle cytosol or by the addition of a high concentration of salt.

A study of some enzymes of glycerolipid biosynthesis in rat liver after subtotal hepatectomy.

1. The accumulation of triglyceride in the liver remnant after subtotal hepatectomy (removal of 82% of the liver) exceeded that described for partial hepatectomy (removal of 70% of the liver). 2. Palmitoyl-CoA synthetase, glycerol phosphate acyltransferase and diglyceride acyltransferase activities were measured in the microsomal fraction, and phosphatidate phosphohydrolase activity was measured in the particle-free supernatant fraction, prepared from the liver remnant at various times after subtotal hepatectomy. 3. The only enzyme showing a significant change in specific activity was phosphatidate phosphohydrolase. The specific activity was approximately fivefold that of the control value at 6h after operation and threefold that of the control at 10, 16 and 24h after operation. A smaller increase in the specific activity of the enzyme in sham-operated animals occurred only at 6h after operation. 4. However, at this time the total phosphohydrolase activity of the remaining liver in the sham-operated rats was approximately threefold that in hepatectomized rats. 5. Injection of actinomycin D prevented the increase in activity of phosphatidate phosphohydrolase but did not prevent the accumulation of triglyceride.