Properties of cytochrome c modified by attachment to a carbohydrate polymer

By enzymic digestion of the polysaccharide part of the covalent complex between cytochrome c and Sephadex G-200, a new water-soluble cytochrome c derivative is obtained (called cytochrome cr). Measurement of the free amino groups of this derivative indicates that on average the molar ratio between cytochrome c and polysaccharide is close to 1. Chemical determination of the sugar content gives a value of approx. 24000 for the molecular weight of cytochrome cr. On these bases the soluble cytochrome cr complex may be thought of as a folded protein to which a long polysaccharide tail is covalently bound. The functional behaviour of cytochrome cr is much more similar to that of the native molecule than to that of the insoluble complex (cytochrome ci). In particular the kinetics of the reaction of cytochrome cr and cytochrome cn (native) with ascorbate, ferrocyanide-ferricyanide, O2 and cytochrome c oxidase were investigated in considerable detail. The results of these experiments, together with the observation that the insoluble complex of cytochrome c is a very poor substrate of cytochrome c oxidase [Colosimo, Brunori & Antonini (1976) Biochem. J. 153, (657-661], indicate that hindrance effects constraining the approach between cytochrome cr and its oxidase are of greater importance than specific chemical modifications in determining the functional behavior of the protein.