UNSATURATED FATTY-ACIDS ASSOCIATED WITH GLYCOGEN MAY INHIBIT GLUCOSE-6 PHOSPHATASE IN RAT-LIVER

This study was conducted to identify the nature of a glycogen-associat ed compound that had been shown to inhibit glucose-6 phosphatase in vi tro. Glycogen was purified from the liver of fed rats by potassium hyd roxyde digestion and ethanol precipitation. It inhibited glucose-6 pho sphatase in microsomes isolated from rats deprived of food for 48 h. T wo glycogen-associated fractions were purified by anion-exchange chrom atography on DOWEX 1 (200-400 mesh). These fractions inhibited microso mal glucose-6-phosphatase activity in vitro (80 +/- 2 and 76 +/- 3% of control, respectively). After chromatography, glycogen was no longer inhibitory (101 +/- 3% of control). Because glycogen is associated wit h endoplasmic reticulum membranes in the liver, we tested the hypothes is that lipids could be involved in the inhibitory process. Lipids wer e extracted from glycogen by Folch's method and analyzed by thin-layer chromatography and gas chromatography. The glycogen-associated fracti ons did not contain complex lipids but contained unsaturated fatty aci ds, which had been shown previously to inhibit glucose-6-phosphatase i n vitro. Because the concentration of unsaturated fatty acids in both fractions quantitatively accounted for the inhibition of glucose-6 pho sphatase observed, and because noninhibitory chromatographed glycogen reconstituted with equivalent amounts of pure unsaturated fatty acids inhibited the enzyme as glycogen did, we conclude that unsaturated fat ty acids likely constitute the glycogen-associated compound that inhib its glucose-6 phosphatase activity.