Fatty acyl-CoA esters inhibit glucose-6-phosphatase in rat liver microsomes.
In native rat liver microsomes glucose 6-phosphatase activity is dependent not only on the activity of the glucose-6-phosphatase enzyme (which is lumenal) but also on the transport of glucose-6-phosphate, phosphate and glucose through the respective translocases T1, T2 and T3. By using enzymic assay techniques, palmitoyl-CoA or CoA was found to inhibit glucose-6-phosphatase activity in intact microsomes. The effect of CoA required ATP and fatty acids to form fatty acyl esters. Increasing concentrations (2-50 microM) of CoA (plus ATP and 20 microM added palmitic acid) or of palmitoyl-CoA progressively decreased glucose-6-phosphatase activity to 50% of the control value. The inhibition lowered the Vmax without significantly changing the Km. A non-hydrolysable analogue of palmitoyl-CoA also inhibited, demonstrating that binding of palmitoyl-CoA rather than hydrolysis produces the inhibition. Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer demonstrated that palmitoyl-CoA alone or CoA plus ATP and palmitic acid altered the microsomal permeability to glucose 6-phosphate, but not to glucose or phosphate, indicating that T1 is the site of palmitoyl-CoA binding and inhibition of glucose-6-phosphatase activity in native microsomes. The type of inhibition found suggests that liver microsomes may comprise vesicles heterogeneous with respect to glucose-6-phosphate translocase(s), i.e. sensitive or insensitive to fatty acid ester inhibition.
Fulceri
R
R
Istituto di Patologia Generale, University of Siena, Italy.
Gamberucci
A
A
Scott
H M
HM
Giunti
R
R
Burchell
A
A
Benedetti
A
A
D000214:Acyl Coenzyme A / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002463:Cell Membrane Permeability; D003600:Cytosol; D004952:Esters; D005952:Glucose-6-Phosphatase / Q000037:antagonists & inhibitors*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000214:Acyl Coenzyme A; D004952:Esters; D005952:Glucose-6-Phosphatase