Pseudoazurin mediates periplasmic electron flow in a mutant strain of Paracoccus denitrificans lacking cytochrome c550

A periplasmic protein able to transfer electrons from cytoplasmic membrane to the periplasmic nitrite reductase (cytochrome cd(1)) has been purified from the anoxically grown cytochrome C-550 mutant strain Pd2121 and shown to be pseudoazurin by several independent criteria (molecular mass, copper content, visible spectrum, N-terminal amino acid sequence). Under our assay conditions, the half-saturation of electron transport occurred at about 10 mu M pseudoazurin; the reaction was retarded by increasing ionic strength. (C) 1999 Federation of European Biochemical Societies.