Characterization of the exchange reactions of rat liver 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase

The Fru-6-P/Fru-2,6-P₂ exchange reaction of rat liver 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase was almost entirely dependent on the presence of P_i. This exchange was not due to a reversal of the bisphosphatase nor to trace amounts of adenine nucleotide in the enzyme. Exchange activity was maximal at pH 7, activated by ADP, and equal to 10-15 percent of the kinase V_max. The ADP ATP exchange reaction was more resistant to various protein modifying agents than the kinase. These studies confirm the existence of both exchange reactions but do not prove they are related to the kinase reaction.