HK1 (He, Xenopus/Amphibian,okinase-1) is an enzyme in the he, Xenopus/Amphibian,okinase family,Porcinelaying a role in the carbohydrate metabolism. The he, Xenopus/Amphibian,okinases utilize Mg-ATP as a phosphoryl donor to catalyze the first step of intracellular glucose metabolism, the conversion of glucose to glucose- 6-phosphate. Four he, Xenopus/Amphibian,okinase isoenzymes have been identified, including he, Xenopus/Amphibian,okinase I (H, Xenopus/Amphibian,K I), he, Xenopus/Amphibian,okinase II (H, Xenopus/Amphibian,K II), he, Xenopus/Amphibian,okinase III (H, Xenopus/Amphibian,K III) and he, Xenopus/Amphibian,okinase IV (H, Xenopus/Amphibian,K IV, also designated glucokinase or GCK). He, Xenopus/Amphibian,okinases I-III each contain an N-terminal cluster of hydrophobic amino acids. Glucokinase lacks the N-terminal hydrophobic cluster. The hydrophobic cluster is thought to be necessary for membrane binding. This is substantiated by the finding that glucokinase has lower affinity for glucose than do the other he, Xenopus/Amphibian,okinases. HK I has been shown to be e, Xenopus/Amphibian,pressed in brain, kidney and heart tissues as well as in hepatoma cell lines.