Kinetic properties of hexokinase under near-physiological conditions. Relation to metabolic arrest in Artemia embryos during anoxia

Previous analyses of glycolytic metabolites in Ar-temia embryos indicate that an acute inhibition of glu-cose phosphorylation occurs during pHi-mediated met-abolic arrest under anoxia. We describe here kinetic features of hexokinase purified from brine shrimp em-bryos in an attempt to explain the molecular basis for this inhibition. At saturating concentrations of cosub-strate, ADP is an uncompetitive inhibitor toward glu-cose and a partial noncompetitive inhibitor toward ATP (Ki, = 0.86 mM, Kii = 1.0 mM, K i d = 1.9 mM). With cosubstrates at subsaturating concentrations, the un-competitive inhibition versus glucose becomes noncom-petitive, while inhibition versus ATP remains partial noncompetitive. The partial noncompetitive inhibition of ADP versus ATP is characterized by a hyperboli