Heme binding and transport--a spectrophotometric study of plasma glycoglobulin hemochromogens.

A hitherto unreported phenomenon is the immediate production of the spectrum of ferrohemochromogens (in the presence of sodium dithionite) upon the addition in vitro of hydroxyhemin (pH 7.6-7.8) to the plasmas or sera, as well as to certain Cohn plasma protein fractions, of all mammalian species thus far examined. This distinctive reaction is characteristic of a coordination complex with heme iron, and is ascribed to a remarkable affinity for heme of certain plasma glycoglobulins, which include hemopexin. Spectrophotometry has permitted estimations of the specific heme-binding capacity (as ferrohemochromogen) of the plasmas, the rate of removal from plasma of injected heme, and the production of bile pigments therefrom. The study leads to a new proposal of the cooperative roles of the glycoglobulin hemochromogens and hematin-albumin in heme transport and bile pigment production.