Storey, K.B. 1980. Regulatory properties of hexokinase from flight muscle of Schaistocerca americana gregaria. Role of the enzyme in control of glycolysis during the rest-to-flight transition. Insect Biochem. 10, 637- 645.

REGULATORY PROPERTIES OF HEXOKINASE FROM FLIGHT MUSCLE OF SCHISTOCERCA AMERICANA GREGARIA. ROLE OF THE ENZYME IN CONTROL OF GLYCOLYSIS DURING THE REST-TO-FLIGHT TRANSITION

KENNETH B. STOREY


Abstract
Hexokinase (E.C. 2.7.1.1) from the flight muscle of the locust, Schistorcerca americana gregaria, was purified to homogeneity by an affinity chromatography method. Hexokinase in locust muscle is a soluble enzyme, occurs as a single isozyme, and has a pI of 5.7, a molecular weight of 97 000 + 4000, and a pH optimum of 7.6 in Tris buffer. Michaelis constants are 0.40 + 0.04, 1.00 + 0.11, and 0.15 + 0.02 mM for ATP, Mg2+, and glucose respectively. ITP, CTP, GTP and UTP were poor phosphate donors for the enzyme but mannose and fructose could substitute for glucose and Mn2+ could satisfy the divalent cation requirement.

High concentrations of K+, NH4+, Li+, SO4 2- and Ca2+ (Ki(Ca2) = -8.5+0.80 mM) were inhibitory. Product inhibition by ADP was non-competitive (Ki = 3.5 + 0.3 mM) with respect to either substrate while product inhibition by glucose-6-P was non-competitive with respect to glucose (Ki = 0.087 + 0.01 mM) and competitive with respect to ATP (Ki = 0.012 + 0.001 mM). Pi, alanine and sn-glycerol-3-P could reverse glucose-6-P inhibition. All three altered the Vmax activity for glucose-6-P inhibited hexokinase while alanine also lowered the apparent Km for ATP. Alanine effects were potentiated by physiological levels of Na+.

The regulation of flight muscle hexokinase in vivo during the rest-to-flight transition is discussed.