Fructose 2,6-bisphosphate as a contaminant of commercially obtained fructose 6-phosphate: Effect on PPi:fructose 6-phosphate phosphotransferase

Fructose 6-phosphate from several commercial sources was shown to be contaminated with fructose 2,6-bisphosphate. This contaminant was identified by its activation of PP_i:fructose 6-phosphate phosphotransferase, extreme acid lability and behaviour on ion-exchange chromatography. The apparent kinetic properties of PP_i:fructose 6-phosphate phosphotransferase from castor bean endosperm were considerably altered when contaminated fructose 6-phosphate was used as a substrate. Varying levels of fructose 2,6-bisphosphate in the substrate may account for differences that have been observed in the properties of the above enzyme from several plant sources.