A hexokinase from fish liver with wide specificity for nucleotides as phosphoryl donor

The liver of rainbow trout contains two hexokinases (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) designated C and D from the elution pattern in DEAE-cellulose column chromatography. Hexokinase D has been purified about 50-fold from the liver of rainbow trout by chromatography with DEAE-cellulose and Sephadex G-200, and by isoelectric focusing. The properties of hexokinase D were similar to those of mammalian hexokinase III with respect to the Km values for ATP and glucose and the substrate inhibition by glucose at high concentration. However, the enzyme showed a wide specificity for nucleotides as the phosphoryl donor. Although it has been reported that the only effective nucleotide as the phosphoryl donor for hexokinase from various origin in ATP, and that ADP, a reaction product, inhibits the enzyme, hexokinase D from the rainbow-trout liver was found to be able to form glucose 6-phosphate (Glc-6-P) from glucose and various nucleotides such as ATP, ADP, CTP, GTP, UTP and UDP. The reaction products from ADP and glucose, Glc-6-P and AMP, were identified by chromatography on ion-exchange resin column and paper. The enzyme D was not inhibited by ADP but was strongly inhibited by AMP, which is a reaction product from ADP.