Acylation Of Glycerophosphate Research Articles

Fatty acid activation and acyl transfer in organs from rats in different nutritional states

1. 1. The activities of the fatty acid activating enzymes, carnitine palmityltransferase and glycerophosphate acylating enzyme(s) have been measured in the liver, heart, and epididymal fat from fed, fasted, glucose-refed, and fat-fed rats. 2. 2. Fasting gave no significant change in the activation of long-chain fatty acids, but glucose-refeeding caused a decreased activation rate in the liver. 3. 3. The activation of short- and medium-chain fatty acids was reduced during fasting in all the investigated organs. Glucose-refeeding increased the activation of heptanoate in the liver and all the short- and medium-chain acids in heart. 4. 4. The carnitine palmityltransferase activity in the liver increased both in fasted and fat-fed animals. Glucose-refeeding normalized the activity. No significant changes were found in the other tissues. 5. 5. The glycerophosphate acylation in the liver and heart decreased during fasting and fat-feeding. After glucose-refeeding the activity in the liver increased again to the level found in the controls. 6. 6. It is suggested that in rat liver the activity of the fatty acid-activating enzymes, the carnitine palmityltransferase and the glycerophosphate acylating enzyme(s) participate in the regulation of fatty acid metabolism. The study gives no conclusive evidence for such mechanisms in the heart or epididymal fat.

The acylation of glycerophosphate in rat liver A new assay procedure for glycerophosphate acylation, studies on its subcellular and submitochondrial localization and determination of the reaction products

1. 1. Glycero phosphate acyltransferase (acyl-CoA: l- glycerol-3- phosphate-O- acyltransferase , EC 2.3.1.15) has been studied in rat liver homogenate and in sub-cellular and submitochondrial fractions with the aid of a new assay procedure for the enzyme. Rat liver homogenates or subfractions were incubated with (−)-palmitylcarnitine, CoA and carnitine palmityltransferase as a donor system for activated fatty acids. sn-[1 (3)- 3H]Glycero-3-phosphate acted as the acyi acceptor. The reaction products were extracted from the incubation mixture with n-butanol. 2. 2. Differential centrifugation of rat liver homogenates showed that the glycerophosphate acyltransf erases has a bimodal intracellular localization. 1/2 to 2/3 of the total activity was found in the mitochondria with the rest in the microsomes. 3. 3. Sucrose density gradient centrifugation confirmed the bimodal intracellular localization revealed by differential centrifugation. 4. 4. Subtractions of mitochondria showed that the glycerophosphate acylation enzymes is localized mainly in the outer membrane. 5. 5. Thin-layer chromatography showed that rat liver homogenate, mitochondria and microsomes gave different reaction products. Mitochondria chiefly produced lysophosphatidic acid and, in addition, some phosphatidic acid and monoglyceride. The chief product of microsomes was phosphatidic acid. In addition, considerable amounts of diglyceride and some monoglyceride were formed. The reaction products obtained with total homogen were quite similar to those of microsomes.

Involvement of Acyl Carrier Protein in Acylation of Glycerol 3-Phosphate in Clostridium butyricum: II. EVIDENCE FOR THE PARTICIPATION OF ACYL THIOESTERS OF ACYL CARRIER PROTEIN

Abstract 1. In order to examine the involvement of acyl carrier protein in the acylation of glycerophosphate by bacterial extracts, a series of experiments with radioactive glycerol 3-phosphate, potential acyl donors, and enzyme preparations from Clostridium butyricum were carried out. 2. The conversion of 14C-glycerophosphate to lipid, mainly lysophosphatidic acid, in the presence of a particulate fraction from C. butyricum was found to be dependent on the addition of acyl carrier protein (ACP) isolated from either C. butyricum or Escherichia coli. The apparent Km was 1.2 x 10-6 m for C. butyricum ACP and 3.4 x 10-6 m for E. coli ACP. Since no source of acyl groups was added in this series of experiments, it is postulated that the acyl groups transferred to glycerophosphate were derived from the particles. 3. With this particulate fraction, chemically synthesized 3H-palmityl-ACP also markedly stimulated the acylation of glycerol 3-phosphate and was an efficient donor of palmitate in the synthesis of lysophosphatidic acid. Palmityl coenzyme A had little effect on glycerophosphate acylation with the particulate fraction as the sole enzyme source. 4. A two-fold stimulation of glycerophosphate acylation by palmityl-CoA was observed when a soluble protein fraction from C. butyricum was added to the particulate fraction. Under these conditions some transfer of labeled fatty acids from 3H-acyl-CoA to 14C-glycerophosphate was observed. The lysophosphatidic acid isolated had 0.3 3H-acyl group per 14C-glycerophosphate. Presumably, the remainder of the acyl groups was derived from the enzyme sources. When ACP was added, the labeled fatty acids derived from acyl-CoA were further diluted by endogenous fatty acids. 5. Sodium lauryl sulfate also stimulated glycerophosphate acylation in the presence of particles from C. butyricum plus the soluble protein fraction. Both palmityl-CoA and sodium lauryl sulfate stimulated glycerophosphate acylation more at 25° than at 30°. These results suggest that some of the effects of palmityl-CoA in this system are the result of its surfactant properties.