Media type: E-Article Title: Midgut mitochondrial transhydrogenase in wandering stage larvae of the tobacco hornworm, Manduca sexta Contributor: Vandock, Kurt P.; Smith, Stan L.; Fioravanti, Carmen F. Published: Wiley, 2008 Published in: Archives of Insect Biochemistry and Physiology, 69 (2008) 3, Seite 118-126 Language: English DOI: 10.1002/arch.20277 ISSN: 0739-4462; 1520-6327 Origination: Footnote: Description: AbstractMidgut 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. Arch. Insect Biochem. Physiol. 69:118‐126, 2008. © 2008 Wiley‐Liss, Inc.