Ecdysone 3-epimerase from the midgut of Manduca sexta (L.). |
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| Authors: | R T Mayer J L Durrant G M Holman G F Weirich J A Svoboda |
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| Institution: | Veterinary Toxicology and Entomology Research Laboratory, Agricultural Research-Science and Education Administration, U. S. Department of Agriculture, College Station, Texas 77840, USA;Insect Physiology Laboratory, Agricultural Research-Science and Education Administration, U. S. Department of Agriculture, Beltsville, Maryland, 20705, USA |
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| Abstract: | Ecdysone 3-epimerase was partially purified by ammonium sulfate fractionation from the 100,000 g supernate of Manduca sexta midguts. The enzyme converts ecdysone and 20-hydroxyecdysone to their respective 3-epimers, requires NADH or NADPH and O2 for this reaction, and has the following kinetic parameters: for ecdysone, Km = 17.0 +/- 1.4 microM, Vmax = 110.6 +/- 14.6 pmol min-1 mg-1; for 20-hydroxyecdysone, Km = 47.3 +/- 7.5 microM, Vmax = 131.0 +/- 3.5 pmol min-1 mg-1: for NADPH, Km = 85.4 +/- 10.6 microM; for NADH, Km = 51.3 +/- 1.3 microM. The reaction is irreversible and can be inhibited by various ecdysteroids. |
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