Ascaris suum hexokinase: purification and possible function in compartmentation of glucose 6-phosphate in muscle

Hexokinase (EC 2.7.1.1) is present in a soluble and a bound form in homogenates of Ascaris suum muscle. Cellulose acetate electrophoresis, isoelectric focusing, and ion exchange chromatography confirmed the presence of only one molecular form of hexokinase in this muscle. A procedure for purifying hexokinase from Ascaris muscle has been developed utilizing ion-exchange chromatography, ammonium sulfate fractionation and gel filtration. The enzyme is a monomer with a molecular weight of 100 000 as determined by sodium dodecyl sulfate gel filtration. The Stokes' radius, diffusion coefficient, and frictional ratio have been determined. The apparent Michaelis constants for glucose and ATP are 4.7-10(-3) M and 2.2-10(-4) M, respectively. Ascaris hexokinase also exhibits end-product inhibition by glucose 6-phosphate and ADP. It is postulated that the kinetic parameters of the enzyme are the results of its function, that of generating glucose 6-phosphate primarily for glycogen synthesis.