Four types of water-soluble cytochromes b-558 (cyt. b-558) have been isolated and purified from blood serum (cyt. b-558 (I), cyt. b-558 (II)) and erythrocyte membranes (cyt. b-558 (III) and cyt. b-558 (IV)). The cytochromes differ in their acid-basic properties, molecular masses (110, 95, 125 and 80 kDa for cyt. b-558 (I), cyt. b-558 (II), b-558 (III) and cyt. b-558 (IV), respectively) as well as by the composition (cyt. b-558 (III) and cyt. b-558 (IV) are lipoproteins) and absorption maxima at the wavelengths of 340-360 nm. The cytochromes have similar absorption maxima at the wavelengths 600-400 nm (560, 530 and 412 nm in the oxidized state) and 558, 525 and 420 nm in the reduced state) which makes them identical to cytochromes b-558 obtained from blood constituents membranes.
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