Abstract
Abstract Homogeneous rabbit liver fructose 1,6-diphosphatase (specific activity of 35 at pH 7.3 and 30°) was activated by various fatty acids, of which oleate was the most effective. In the absence of oleate or other activators, the enzyme had a pH optimum at 8.4 with either Mn2+ or Mg2+. The addition of oleate imposed additional neutral activity onto the activity observed in its absence. Activation by oleate was half-maximal at a concentration of 4 µm and had a pH optimum of 7.1 with either metal. Oleate or 3-phosphoglycerate protected the enzyme from inactivation by ATP and ADP. Half-maximal protection against inactivation by 1.5 mm ATP was found with either 9 µm oleate or 90 µm 3-phosphoglycerate. AMP inhibition of the oleate-protected or untreated enzyme was cooperative, with 50% inhibition observed at 17 µm AMP. In contrast, the ATP-inactivated enzyme showed noncooperative AMP inhibition with a Ki of 7 µm. Physical interaction of fructose 1,6-diphosphatase and oleate was supported by demonstration of the solubilization of [14C]oleic acid adsorbed on Celite. Fatty acids appear to be unique among physiologically occurring effectors of fructose 1,6-diphosphatase in that they serve as potent activators and also protect the enzyme from ATP inactivation.
Published Version
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