Effect of salts on the activity of carrot phosphofructokinase

Phosphofructokinase (EC 2.7.1.11) from carrot roots was activated by a number of salts. Increase in salt concentration beyond the optimum generally led to a decrease in enzyme activity. Salts of the multivalent anions sulfate and phosphate were very effective activators and inhibitors. Potassium acetate and potassium succinate were also activators. Potassium tartrate and potassium citrate produced a small stimulation at low concentration but with further increase they became inhibitory. The results suggested that the salt effect was largely due to anions rather than cations. Salts such as NaCl, KCl, and in particular potassium phosphate, relieved the inhibition of carrot phosphofructokinase by phosphoenolpyruvate. KCl and potassium phosphate also reversed the inhibition of carrot phosphofructokinase by citrate. The possible significance of these observations in the regulation of glycolysis and carbohydrate metabolism, and in salt respiration is discussed.