Midgut mitochondrial transhydrogenase in wandering stage larvae of the tobacco hornworm, Manduca sexta.
Midgut mitochondria from fifth larval instar Manduca sexta exhibited a transhydrogenase that catalyzes the following reversible reaction: NADPH + NAD(+) <--> NADP(+) + NADH. The NADPH-forming transhydrogenation occurred as a nonenergy- and energy-linked activity. Energy for the latter was derived from the electron transport-dependent utilization of NADH or succinate, or from Mg++-dependent ATP hydrolysis by ATPase. The NADH-forming and all of the NADPH-forming reactions appeared optimal at pH 7.5, were stable to prolonged dialysis, and displayed thermal lability. N,N'-dicyclohexylcarbodiimide (DCCD) inhibited the NADPH --> NAD(+) and energy-linked NADH --> NADP(+) transhydrogenations, but not the nonenergy-linked NADH --> NADP(+) reaction. Oligomycin only inhibited the ATP-dependent energy-linked activity. The NADH-forming, nonenergy-linked NADPH-forming, and the energy-linked NADPH-forming activities were membrane-associated in M. sexta mitochondria. This is the first demonstration of the reversibility of the M. sexta mitochondrial transhydrogenase and, more importantly, the occurrence of nonenergy-linked and energy-linked NADH --> NADP(+) transhydrogenations. The potential relationship of the transhydrogenase to the mitochondrial, NADPH-utilizing ecdysone-20 monooxygenase of M. sexta is considered.
Vandock
Kurt P
KP
Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
Smith
Stan L
SL
Fioravanti
Carmen F
CF
D000818:Animals; D003956:Dialysis; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D041981:Gastrointestinal Tract / Q000201:enzymology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007814:Larva / Q000201:enzymology; D018402:Manduca / Q000201:enzymology*; D009250:NADP Transhydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology
D009840:Oligomycins; D004024:Dicyclohexylcarbodiimide; D009250:NADP Transhydrogenases