Molybdopterin cytosine dinucleotide

The degradation of isoquinoline by Pseudomonas diminuta strain 7 is initiated by an oxidoreductase that contains [2Fe-2S] centers and the cofactor molybdopterin cytosine dinucleotide (Lehmann et al. 1994). 

They have a molecular mass of 300-360 kDa, and contain per molecule, eight atoms of Fe, eight atoms of acid-labile S, two atoms of Mo, and two molecules of FAD. The organic component of the pterin molybdenum cofactor is generally molybdopterin cytosine dinucleotide (Hetterich et al. 1991 Schach et al. 1995). 

Figure 16-31 (A) Structure of molybdopterin cytosine dinucleotide complexed with an atom of molybdenum. (B) Stereoscopic ribbon drawing of the structure of one subunit of the xanthine oxidase-related aldehyde oxidoreductase from Desulfo-vibrio gigas. Each 907-residue subunit of the homodimeric protein contains two Fe2S2 clusters visible at the top and the molybdenum-molybdopterin coenzyme buried in the center. (C) Alpha-carbon plot of portions of the protein surrounding the molybdenum-molybdopterin cytosine dinucleotide and (at the top) the two plant-ferredoxin-like Fe2S2 clusters. Each of these is held by a separate structural domain of the protein. Two additional domains bind the molybdopterin coenzyme and there is also an intermediate connecting domain. In xanthine oxidase the latter presumably has the FAD binding site which is lacking in the D. gigas enzyme. From Romao et al.633 Courtesy of R. Huber.

The recognition that the Mo in the molybdoproteins exists in organic cofactor forms came from studies of mutants of Aspergillus and Neurospora.650 In 1964, Pateman and associates discovered mutants that lacked both nitrate reductase and xanthine dehydrogenase. Later, it was shown that acid-treated molybdoenzymes released a material that would restore activity to the inactived nitrate reductase from the mutant organisms. This new coenzyme, a phosphate ester of molybdopterin (Fig. 15-17), was characterized by Rajagopalan and coworkers.650 651 A more complex form of the coenzyme, molybdopterin cytosine dinucleotide... 

MPT, molybdopterin mononucleotide MPTpG, molybdopterin guanine dinucleotide MPTpC, molybdopterin cytosine dinucleotide. b Assignment based on the abstraction of S by CN. ... 

MCD molybdopterin cytosine dinucleotide or magnetic circular dichroism... 

MPD = Molybdopterin MCD = Molybdopterin cytosine dinucleotide MGD = Molybdopterin guanine dinucleotide. 

Fig. 5 Active site of MoCu-CODH (a) and Ni-CODH (b). The bidentate sulfur ligands of the MoCu-CODH denoted by So are part of a molybdopterin cytosine dinucleotide cofactor. Sj denotes an inorganic sulfide ligand...

The membrane-bound PQQ-alcohol dehydrogenase (ADH) is to be considered the key enzyme in the production of vinegar because of its essential place in the oxidation of ethanol to acetaldehyde, the intermediate that will be later oxidized by the MCD (molybdopterin cytosine dinucleotide)-aldehyde dehydrogenase (ALDH) to acetic acid. This idea is based on the finding that a defect in membrane-bound ADH has been associated with a reduction in acetic acid resistance (Chinnawirotpisan et al. 2003 Okumura et al. 1985 Takemura et al. 1991). Additionally, the elevation in membrane-bound ALDH activity by gene amplification has been reported to enhance the acetic acid concentration finally attained in Acetobacter (Fukaya et al. 1989). 

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