Identification of the missing component in the mitochondrial benzamidoxime prodrug-converting system as a novel molybdenum enzyme.
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Havemeyer A, Bittner F, Wollers S, Mendel R, Kunze T, Clement B
Identification of the missing component in the mitochondrial benzamidoxime prodrug-converting system as a novel molybdenum enzyme.
J Biol Chem. 2006 Nov 17;281(46):34796-802. Epub 2006 Sep 13.
- PubMed ID
- 16973608 [ View in PubMed]
- Abstract
Amidoximes can be used as prodrugs for amidines and related functional groups to enhance their intestinal absorption. These prodrugs are reduced to their active amidines. Other N-hydroxylated structures are mutagenic or responsible for toxic effects of drugs and are detoxified by reduction. In this study, a N-reductive enzyme system of pig liver mitochondria using benzamidoxime as a model substrate was identified. A protein fraction free from cytochrome b5 and cytochrome b5 reductase was purified, enhancing 250-fold the minor benzamidoxime-reductase activity catalyzed by the membrane-bound cytochrome b5/NADH cytochrome b5 reductase system. This fraction contained a 35-kDa protein with homologies to the C-terminal domain of the human molybdenum cofactor sulfurase. Here it was demonstrated that this 35-kDa protein contains molybdenum cofactor and forms the hitherto ill defined third component of the N-reductive complex in the outer mitochondrial membrane. Thus, the 35-kDa protein represents a novel group of molybdenum proteins in eukaryotes as it forms the catalytic part of a three-component enzyme complex consisting of separate proteins. Supporting these findings, recombinant C-terminal domain of the human molybdenum cofactor sulfurase exhibited N-reductive activity in vitro, which was strictly dependent on molybdenum cofactor.