Discriminant responses of the catalytic unit and glucose 6-phosphate transporter components of the hepatic glucose-6-phosphatase system in Ehrlich ascites-tumor-bearing mice.
The effect of Ehrlich ascites tumor cells, in vivo, on the hepatic glucose-6-phosphatase (G6Pase) system was examined. The V(max) for glucose 6-phosphate hydrolysis by G6Pase was reduced by 40% and a greater than 15-fold decrease in mRNA encoding the catalytic unit of the G6Pase system was observed 8 days after injection with tumor cells. Blood glucose concentration was decreased from 169 +/- 17 to 105 +/- 9 mg/dl in tumor-bearing mice. There was no change in the G6P transporter (G6PT) mRNA level. However, there was a significant decrease in G6P accumulation into hepatic microsomal vesicles derived from tumor-bearing mice. Decreased G6P accumulation was also associated with a decrease in G6Pase hydrolytic activity in the presence of vanadate, a potent catalytic-unit inhibitor. In addition, G6P accumulation was nearly abolished in microsomes treated with N-bromoacetylethanolamine phosphate, an irreversible inhibitor of the G6PT. These results demonstrate that the catalytic unit and G6PT components of the G6Pase system can be discriminantly regulated, and that microsomal glucose 6-phosphate uptake is dependent on catalytic unit activity as well as G6PT action.
Foster
J D
JD
Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine and Health Sciences, 501 North Columbia Road, Grand Forks, North Dakota 58203, USA. foster@medicine.nodak.edu
Wiedemann
J M
JM
Pan
C J
CJ
Chou
J Y
JY
Nordlie
R C
RC
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D004983:Ethanolamines / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019298:Glucose-6-Phosphate / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008862:Microsomes, Liver / Q000201:enzymology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism
D001786:Blood Glucose; D004983:Ethanolamines; D012333:RNA, Messenger; D012334:RNA, Neoplasm; C020161:N-bromoacetylethanolamine phosphate; D019298:Glucose-6-Phosphate; D005952:Glucose-6-Phosphatase