ON THE MOLECULAR WEIGHT OF CYTOCHROME c FROM MAMMALIAN HEART MUSCLE

Abstract

Cytochrome c, a conjugated protein containing iron protoporphyrin IX as the prosthetic group, is an important intermediary catalyst in tissue respiration (see Oppenheimer and Stern (1)).It is water-soluble, readily extracted from certain animal and plant tissues as well as microorganisms, and stable in purified form.Although its structure and physicochemical properties, e.g.absorption spectrum, magnetic moment, and catalytic activity, have been extensively studied (see Lemberg and Legge ( 2)), only scanty information is available on its molecular size and shape (3-6).Some of the values quoted in these reviews refer to unpublished experiments, and no sedimentation or diffusion diagrams appear to have been presented thus far.The object of the present study was to obtain quantitative information on the molecular weight and related parameters of ferricytochrome c from mammalian heart tissue.Highly purified preparations from several species (horse, beef, pig) were kindly placed at our disposal by Dr. H. Tint and Dr. W. Reiss of the Wyeth Institute of Applied Biochemistry, Philadelphia.These investigators have previously determined the electrophoretie homogeneity, spectrophotometric constants, and iron content of the same cytochrome preparations (7).The minimal molecular weight was calculated from these data ((7) p. 397) on the assumption that 1 atom of iron, in the form of a heme group, is present in 1 molecule of the conjugated protein.In the present experiments, the molecular weight was derived from sedimentation velocity and diffusion measurements by means of Svedberg's formula.The values thus obtained are independent of any assumptions as to the iron or heme content of the cytochrome c molecule.EXPERIMENTAL Methods and Materials-The ferricytochrome c preparations employed in these experiments had been stored for approximately 2 years at about 4' in 0.14 M NaCl solutions, with small amounts of Merthiolate added as a