EFFECT OF VANADATE ON THE ACTIVITY OF RAT JEJUNAL 6-PHOSPHOFRUCTO-1-KINASE

The effect of sodium orthovanadate on the activity of 6 phosphofructo- 1-kinase (PFK) in the epithelial cells of rat: small intestine was inv estigated. Injection of vanadate (2.5 mg/rat) into rats at 2-day inter vals per week for two consecutive weeks resulted in a significant decr ease in the maximal activities and activity ratios (activity at 0.5 mM fructose-6-phosphate at pH 7.0/activity at pH 8.0 [v(0.5)/V]) of the partially purified PFK in rat jejunum. Also, the sensitivity of jejuna l PFK to inhibition by ATP increased in rats treated with vanadate. Th e addition of 1 mu M fructose-2,6-biphosphate and 50 mu M AMP in the a ssays released the enzyme inhibition by ATP, and no significant differ ence was seen between vanadate-injected and control rats. Moreover, th e extent of activation with 1 mu M fructose-2,6-bisphosphate was signi ficantly higher (79%) in vanadate-injected rats than in control rats ( 26%). The present results indicate that rat jejunal PFK is highly inhi bited with vanadate in vivo. Therefore, although vanadate has been con sidered to be an insulin-like agent, because of its insulin like effec ts on adipocytes and skeletal muscle, the present results may indicate that this behavior could not be applicable to normal rat tissues, bec ause the effect of vanadate on jejunal PFK is clearly opposite that of insulin. Copyright (C) 1996 Elsevier Science Inc.