Inhibition studies of glucokinase were carried out with the products of the reaction, glucose 6-phosphate and MgADP-, as well as with ADP3-, Mg2+ and ATP4-. The results of these, together with those of kinetic studies of the uninhibited reaction described previously [Storer & Cornish-Bowden (1976) Biochem. J. 159, 7-14], indicate that the enzyme obeys a ‘mnemonical’ mechanism. This implies that the co-operativity observed with glucose as substrate arises because glucose binds differentially to two forms of the free enzyme that are not in equilibrium under steady-state conditions. The mechanism predicts the decrease in glucose co-operativity observed at low concentrations of MgATP2-. The product-inhibition results suggest that glucose 6-phosphate is released first and that it is possibly displaced by MgATP2- in a concerted reaction.

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