CARBAMOYL-PHOSPHATE AND UREAGENESIS ARE NOT INVOLVED IN AMINO-ACID-STIMULATED GLYCOGENESIS

Amino acids are known to stimulate glycogen synthesis via an increase in cell volume [Baquet, A., Hue, L., Meijer, A, J., van Woerkom, G. M. & Plomp, P. J. A. M. (1990) J. Biol. Chem. 265, 955-959]. It has rece ntly been postulated, however, that carbamoyl phosphate, an intermedia te of ureagenesis, can function as a substrate for glucose phosphoryla tion via carbamoyl-phosphate:glucose phosphotransferase activity of th e glucose-6-phosphatase system. This hypothesis would account for the stimulation of glycogenesis by amino acids such as glutamine and proli ne [Bode, A. M. & Nordlie, R. C. (1993) J. Biol. Chem. 268, 16298-1630 1]. To further examine the role carbamoyl phosphate may play in glycog enesis, isolated hepatocytes were incubated under a variety of conditi ons to manipulate ureagenesis, glycogenesis and carbamoyl-phosphate le vels. Our data indicate that carbamoyl-phosphate levels do not correla te with amino-acid-stimulated glycogenesis and that ureagenesis and gl ycogenesis are not competing metabolic pathways.