Physiological relevance, localization and substrate specificity of the alternative (type II) mitochondrial NADH dehydrogenases of Ogataea parapolymorpha
H. Jürgens (TU Delft - Applied Sciences)
A. Mielgo Gomez (TU Delft - Applied Sciences)
A. Godoy Hernandez (TU Delft - Applied Sciences)
J. ter Horst (TU Delft - Applied Sciences)
J.M. Nijenhuis (Student TU Delft)
D.G.G. McMillan (TU Delft - Applied Sciences, University of Reading)
R. Mans (TU Delft - Applied Sciences)
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Abstract
Mitochondria from Ogataea parapolymorpha harbor a branched electron-transport chain containing a proton-pumping Complex I NADH dehydrogenase and three Type II NADH dehydrogenases (NDH-2). To investigate the physiological role, localization and substrate specificity of these enzymes, the growth of various NADH dehydrogenase knockout mutants was quantitatively characterized in shake-flask and chemostat cultures, followed by oxygen-uptake experiments with isolated mitochondria. NAD(P)H:quinone oxidoreduction of the three NDH-2 were individually assessed. Our findings reveal that the O. parapolymorpha respiratory chain contains an internal NADH-accepting NDH-2 (Ndh2-1/OpNdi1), at least one external NAD(P)H-accepting enzyme, and likely additional mechanisms for respiration-linked oxidation of cytosolic NADH. Metabolic regulation appears to prevent competition between OpNdi1 and Complex I for mitochondrial NADH. With the exception of OpNdi1, the respiratory chain of O. parapolymorpha exhibits metabolic redundancy and tolerates deletion of multiple NADH-dehydrogenase genes without compromising fully respiratory metabolism.
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