The “albumin” fraction of bovine milk—IV. A physico-chemical study of Red Protein A

Abstract

A well-defined major fraction of the red protein from bovine milk has been characterized physico-chemically. A high degree of homogeneity is indicated by the sedimentation diagrams, by the straight line Fujita plots and the reasonable correspondence between diffusion coefficients from low and high speed spinning in the ultracentrifuge and by the absence of any drift in Archibald molecular weights with time. The protein possesses a molecular weight of 93,000±3000, and hydro-dynamic methods indicate that the molecule behaves as a compact prolate ellipsoid of rotation of axial ratio 6 and is only weakly hydrated. Preliminary optical rotation measurements indicate great similarity with other Fe-containing proteins, the prominent absorption band predominantly affecting rotatory behaviour over the same wavelength region; at more distant wavelengths the optical rotation appears to be typical of a native corpuscular protein.