A source of apparent pyrophosphate:fructose 6-phosphate phosphotransferase activity in rabbit muscle phosphofructokinase.

In the presence of UDPglucose, rabbit muscle phosphofructokinase appeared to use PPi as a phosphoryl donor, as reported previously (Biochem. Biophys. Res. Commun. 121, 842-847). This apparent activity was due to conversion of UDPglucose and PPi to glucose 1-phosphate and UTP, the latter being metabolized by phosphofructokinase. Auxiliary enzymes used in the assays were contaminated by UDPglucose pyrophosphorylase. This contamination was sufficient to account for, and had similar properties to, the apparent PPi-dependent activity. Without auxiliary enzymes phosphofructokinase could not use PPi. These findings indicate that the apparent interconversion of phosphofructokinase and PPi:fructose 6-phosphate phosphotransferase must be re-assessed.