Azurin: A Copper Protein Found in Bordetella

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Abstract
SUMMARY: All strains of Bordetella pertussis, B. bronchiseptica and B. parapertussis tested, were found to contain a blue protein; this has been named ‘Azurin’. It has been extracted from the cells of all three species and it has also been isolated from culture supernatant fluids of B. pertussis. The azurin was purified by chromatography on ion-exchange cellulose derivatives and obtained in physically pure form; the materials from each species were identical. In one strain of B. bronchiseptica azurin comprised 0·1% of the bacterial dry weight. Azurin is a water-soluble autoxidizable protein of high oxidation-reduction potential (+395 mV.). It has an absorption maximum at 625 mμ in the oxidized form, with a millimolar extinction coefficient of 3·5 × 103. It contains 0·45% copper which can be completely removed by dialysis against cyanide. The molecular weight is 14,600 (S20,w = 1·58 × 10-13, D20, w = 10·6 × 10-7). Azurin can be reduced by cysteine, glutathione and other reducing agents; the blue colour disappears on reduction. Azurin undergoes reduction in the presence of concentrated cell-free extracts of B. bronchiseptica and succinate, and is reoxidized on aeration.