Effects of 20-Hydroxyecdysone on the Reversible Mitochondrial Transhydrogenase in the Tobacco Hornworm, Manduca sexta

The reversible, mitochondrial membrane-associated transhydrogenase from the midgut of Manduca sexta (L.) (Lepidoptera: Sphingidae) catalyzes hydride-ion transfer between NADP(H) and NAD(H). The effects of ecdysone and 20-hydroxyecdysone were evaluated and compared to both the NADH-NADP and NADPH-NAD transhydrogenations. In the direction of NADPHformation, the developmentally significant transhydrogenations occur as non-energyor energylinked reactions. The energy-linked activity couples with either electron transport-dependent NADH or succinate utilization, or ATP hydrolysis by Mg-dependent ATPase. Upon the addition of ecdysone alone, all energy-linked reactions in the direction of NADPH formation exhibited a notable increase in activity level over the control reaction. The addition of 20hydroxyecdysone yielded no significant increase in the activity of any of the transhydrogenations. Synergistic addition of both ecdysone and 20-hydroxyecdysone resulted in no significant effect on transhydrogenase activity. The results of this study make evident a relationship between the presence of ecdysone and 20-hydroxyecdysone on the overall activity of M. sexta midgut mitochondrial transhydrogenations. The potential mediation of the energy-linked mitochondrial transhydrogenations involved with NADPH synthesis through the developmental relationship of ecdysone and 20-hydroxyecdysone is considered.