Functional organization of mammalian hexokinase II. Retention of catalytic and regulatory functions in both the NH2- and COOH-terminal halves.

Ardehali H, Yano Y, Printz RL, Koch S, Whitesell RR, May JM, Granner DK
J Biol Chem. 1996 271 (4): 1849-52

PMID: 8567628 · DOI:10.1074/jbc.271.4.1849

The mammalian hexokinase (HK) family includes three closely related 100-kDa isoforms (HKI-III) that are thought to have arisen from a common 50-kDa precursor by gene duplication and tandem ligation. Previous studies of HKI indicated that a glucose 6-phosphate (Glu-6-P)-regulated catalytic site resides in the COOH-terminal half of the molecule and that the NH2-terminal half contains only a Glu-6-P binding site. In contrast, we now show that proteins representing both halves of human and rat HKII have catalytic activity and that each is inhibited by Glu-6-P. The intact enzyme and the NH2- and COOH-terminal halves of the enzyme each increase glucose utilization when expressed in Xenopus oocytes. Mutations corresponding to either Asp-209 or Asp-657 in the intact enzyme completely inactivate the NH2- and COOH-terminal half enzymes, respectively. Mutation of either of these sites results in a 50% reduction of activity in the 100-kDa enzyme. Mutation of both sites results in a complete loss of activity. This suggests that each half of the HKII molecule retains catalytic activity within the 100-kDa protein. These observations indicate that HKI and HKII are functionally distinct and have evolved differently.

MeSH Terms (15)

Animals Base Sequence Biological Evolution DNA Primers Glucose Glucosephosphates Hexokinase Humans Kinetics Molecular Sequence Data Mutagenesis, Site-Directed Rats Recombinant Proteins Structure-Activity Relationship Xenopus laevis

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