Kinetic properties of purified aldolase from flight muscle of Schistocerca americana gregaria. Role of the enzyme in the transition from carbohydrate to lipid-fueled flight

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Aldolase (E.C.4.1.2.13) from the flight muscle of the locust, Schistocerca americana gregaria, was purified to homogeneity using phosphocellulose affinity chromatography. The activity of the enzyme (13 units/g wet wt.) was one of the lowest of the glycolytic enzymes in flight muscle. The enzyme has a molecular weight of 155,000 ± 5000, a pI of 4.9 ± 0.5, a pH optimum of 7.3 in Tris buffer, and a K m for fructose-1.6-P 2 of 4.0 ± 0.5 μM. The enzyme resembles muscle aldolases from other sources in displaying a V max activity ratio ( V fructose-1,6-P 2 V fructose-1-P ) of 37. The enzyme was inhibited by the adenylates (ATP, ADP, AMP), NAD +, NADH, excess Mg 2+ and Mn 2+, citrate, and palmitoyl-carnitine. Only citrate (K i = 1.88 ± 0.20 mM) and palmitoyl-carnitine (K i = 18 ± 4 μM) appear to be significant effectors of the enzyme in vivo. Inhibition by these two compounds was mixed competitive with respect to fructose-1,6-P 2. Citrate and palmitoyl-carnitine inhibitions of aldolase may be the signals used to inhibit flight muscle glycolysis during lipid oxidation. The central role of aldolase in the transition from short-term, carbohydrate based flight to long-term, lipid-based flight in the locust is discussed.