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 investigated. Injection of vanadate (2.5 mg/rat) into rats at 2-day intervals per week for two consecutive weeks resulted in a significant decrease in the maximal activities and activity ratios (activity at 0.5 mM fructose-6-phosphate at pH 7.0/activity at pH 8.0 [v0.5/V]) of the partially purified PFK in rat jejunum. Also, the sensitivity of jejunal PFK to inhibition by ATP increased in rats treated with vanadate. The addition of 1 microM fructose-2,6-biphosphate and 50 microM AMP in the assays released the enzyme inhibition by ATP, and no significant difference was seen between vanadate-injected and control rats. Moreover, the extent of activation with 1 microM fructose-2,6-bisphosphate was significantly higher (79%) in vanadate-injected rats than in control rats (26%). The present results indicate that rat jejunal PFK is highly inhibited with vanadate in vivo. Therefore, although vanadate has been considered to be an insulin-like agent, because of its insulin-like effects on adipocytes and skeletal muscle, the present results may indicate that this behavior could not be applicable to normal rat tissues, because the effect of vanadate on jejunal PFK is clearly opposite that of insulin.