A possible role of Z protein in dietary control of hepatic triacylglycerol synthesis.

Abstract

SummaryThe effects of fasting and refeeding on hepatic Z protein were investigated in rats. When [U-14C]palmityl-CoA was added to the liver cytosol fraction from fat-free refed rats, more binding of labeled palmityl-CoA to the Z-protein region was found than in the case of fasted rats. Also the radioactivities in specific precipitations of the palmityl-CoA binding protein with anti-Z immunoglobulin G were higher in the refed rats. The Z protein which stimulated diacylglycerol acyltransferase may be involved in the change of triacylglycerol synthesis in fasted and refed rat livers. Keywords Z protein, diacylglycerol acyltransferase, fasting and refeed ing Although the individual reactions in microsomal pathways of triacylglycerol synthesis in liver and other tissues are well defined (1-3), the factors which regulate the overall rate of liver triacylglycerol formation are not yet clear. Fallon et al. demonstrated that in rats fed on a high carbohydrate diet triacylglycerol formation in liver increased and correlated well with the activities of microsomal glycerophos phate acyltransferase and phosphatidate phosphatase (3-5). On the other hand, in a previous study using rat liver slices it was shown that triacylglycerol synthesis was markedly affected by fasting or refeeding the animals, phospholipid synthesis being virtually constant (6). It was suggested from the results that the syntheses of triacylglycerols and phospholipids are independently controlled. In view of the fact that triacylglycerols and phospholipids in liver are synthesized from a glycerophosphate to 1, 2-diacylglycerol in a common pathway (1), it seems reasonable to postulate that the synthesis of both lipids is regulated after the 1, 2 -diacylglycerol step rather than during the common steps. The present report provides evidence that the binding activity of palmityl-CoA to the Z protein, which is present in the cytosol of liver (7-9) and stimulates the activity of diacylglycerol acyltransferase (10), was higher in refed rats than in fasted rats.

Direct Desaturation of Free Myristic Acid by Hen Liver Microsomal Δ9-Desaturase without Prior Activation to Myristoyl-CoA Derivative

“…The decrease in the desaturase specific activity was directly related with the decrease in concentration of the myristic acid−FABP complex. Previous studies reported that hepatic fatty acid binding protein (hFABP) may specifically direct the utilization of fatty acids toward either esterification ( , ) or oxidative paths (). Albumin was an ineffective replacer of hFABP in stimulating the activity of some microsomal enzymes utilizing fatty acids ( , ).…”

“…Previous studies reported that hepatic fatty acid binding protein (hFABP) may specifically direct the utilization of fatty acids toward either esterification ( , ) or oxidative paths (). Albumin was an ineffective replacer of hFABP in stimulating the activity of some microsomal enzymes utilizing fatty acids ( , ). This suggested the role of FABP in providing fatty acids to their enzymes may be more than a substrate solubilizer.…”

Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling

“…acylCoA :glycerol-3-phosphate acyltransferase [116][117][118], diacylglycerol acyltransferase [119,120], lysophosphatidic acid acyltransferase [121] and acyl-CoA :cholesterol acyltransferase [122,123]. Rat liver FABP appears to have both stimulatory and inhibitory effects on both mitochondrial and microsomal acylCoA synthetases [117,[124][125][126].…”

Possible Roles of Long-chain Fatty Acyl-CoA Esters in the Fusion of Biomembranes

“…FABPs have been shown to enhance the activity of several microsomal acyl-CoA utilizing enzymes involved in cholesterolester-, phospholipid-and triacylglycerol synthesis, i.e. acyl-CoA:glycerol-3-phosphate acyltransferase (Jolly et al, 1997;Haq et al, 1987;Burnett et al, 1979;Mishkin and Turcotte, 1974b) diacylglycerol acyltransferase (Iritani et al, 1980;O'Doherty and Kuksis, 1975) lysophosphatidic acid acyltransferase (Bordewick et al, 1985), and acyl-CoA: cholesterol acyltransferase (Scallen et al, 1985;Grinstead et al, 1983). Rat liver FABP appears to have both stimulatory and inhibitory effects on both mitochondrial and microsomal acyl-CoA synthetases (Noy et al, 1986;Burnett et al, 1979;Ockner and Manning, 1976;Wu-Rideout et al, 1976).…”