Ecdysone oxidase: reaction and specificity.

Ecdysone oxidase oxidizes 3-hydroxysteroids of the excysteroid type irreversibly to 3-dehydro derivatives. The hydrogen of the steroid is transferred by the enzyme to oxygen which is reduced to hydrogen peroxide. Ecdysone oxidase is relatively specific for ecdysone and ecdysterone. Apparent Michaelis constants for these two physiological substrates are 98 and 31 micron, respectively. Cholesterol oxidase and 3alpha-hydroxysteroid and 3beta-hydroxysteroid dehydrogenases which catalyze similar reactions are unable to oxidize ecdysteroids.