Flavodoxins

Flavodoxins

Flavodoxins -

Flavodoxins have been isolated and crystallized from a number of bacteria, including Clostridium pasteurianum, Azotobacter vinelandii and Rhodospirillum rubrum. Their molecular weight ranges from 14,600 to 23,000. The flavodoxin of A. vinelandii is called azotoflavin. It functions as an electron carrier for nitrogen fixation.

The electron transport chain of A.vinelandii consists of Azotobacter ferredoxin, a soluble heat labile component, and azotoflavin. These components constitute a chain between NADPH and nitrogenase.

Flavodoxins do not have metals or labile sulphide. Their chromophore is FMN, and they contain one mole per mole of protein. Flavodoxins are yellow in the oxidized form and blue in partially reduced preparations.

They can accept two electrons, each at a different level of oxidation. Flavodoxins have a high percentage of acidic amino acids. The probable binding site of FMN in flavodoxin is cysteine. The active center is probably located in the each region of flavodoxin.

Most flavodoxins contain 120-150 amino acid residues, corresponding to a molecular weight of about 15,000 (R. rubrum, MW 23,000). Flavodoxins from different species have similar, but never identical, amino acid compositions.

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