Isolation and characterization of polyferredoxin from Methanobacterium thermoautotrophicum The mvhb gene product of the methylviologen‐reducing hydrogenase operon

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Abstract
The methylviologen-reducing hydrogenase operon of Methanobacterium thermoautotrophicum contains an open reading frame. mvhB, the product or which was predicted to have a molecular weight of 44 kDa and to contain as many as 48 iron atoms in 12 [4Fe-4S] clusters, and was therefore suggested to be a polyrerredoxin. We have now, for the first time, isolated this polyfarradoxin. Its identity with the mvhB gene product was evidenced by a comparison of the N-terminal amino acid sequence. The dark-brown protein of apparent molecular weight 44 kDa was found to contain 53 mol Fe and 43 mol acid-labile sulfur per mol. The UV/visible spectrum showed two maxima at 280 nm and 390 nm, and a shoulder at 308 nm. The A 390/A 280 ratio was 0.73. The molar extinction coefficient at 390 nm was 170,000 M−1 cm−1. In the dithionite reduced State the protein displayed an EPR spectrum like that of [4Fe-4S] clusters. The results indicate that the mvhB gene product is indeed a polyferredoxin.