In vitro phosphorylation of purified transketolase by protein kinase C

Abstract

Catalytically active transketolase was purified from rat liver cytosolic fraction by more than 120-fold to near homogeneity by successive column chromatography using DEAE-Sephacel, hydroxylapatite and Mono P matrices. The purified transketolase was rapidly phosphorylated by protein kinase C (PKC) while it was minimally phosphorylated by cAMP-dependent protein kinase and casein kinase II. Phosphoamino acid analysis of the 32P-labeled enzyme revealed that only threonine residue was phosphorylated by PKC. The phosphorylated enzyme became less active (about 40%) than the non-phosphorylated counterpart. Our data suggest that transketolase can be phosphorylated by PKC, which could represent a new type of regulatory mechanism for transketolase.