Molecular Size, Shape, and Homogeneity of the Rabbit Papilloma Virus Protein

In 1937 a protein material was isolated (1) by ultracentrifugation from extracts of warts (2) occurring naturally in Western cottontail rabbits. Readily purified by alternate low and high speed centrifugation the material sediments in the analytical ultracentrifuge with the sharp boundary indicative of high homogeneity and with a sedimentation constant determined only approximately in previous studies to be of the order of 250 X lo-l3 cm. sec.-l dynes-l (1). Investigation of this heavy protein in the past 3 years has shown it to possess with a remarkable degree of uniformity the biological properties ascribable to the rabbit papilloma virus, as demonstrated by quantitative studies on infectivity, complement fixation, and neutralization with specific immune serum (3). Limited by the small quantities of it available, studies of the physical and chemical properties of the protein have been few. Recently, however, enough of it was obtained for studies (4) in the Tiselius apparatus, and the results showed electrophoretic homogeneity of the protein equal to that of hemocyanins (5) and low molecular weight crystalline proteins studied by this method (6). In the present work, studies have been made to obtain information relative to the molecular size, shape, and homogeneity of the protein. For this purpose two methods have been employed, consisting in the combination of diffusion measurements with (1) sedimentation and (2) viscosity data. The latter analysis is of especial interest, since it has recently been shown (7) to furnish information with respect to the size and shape of homogeneous