Structure of the Tobacco Mosaic Virus Particle; Polymerization of Tobacco

Abstract

The chapter describes a critical analysis of the molecular weight of tobacco mosaic virus (TMV) and with polymerization of TMV protein. TMV has a very high molecular weight and measurements of double refraction of flow led to the conclusion that the particles are rod-shaped. The molecular weight of TMV has been determined adequately by physicochemical methods and measurements with the electron microscope. These yielded with fair uniformity a value close to 40 million. A value of about 23 Å for the pitch of the helix of the virus was determined from X-ray diffraction measurements, and pertains to the virus in wet gels. In the determination of molecular weight with the electron microscope, it is desirable to utilize a technique that does not depend upon the retention of the wet particle dimensions. Some of the earliest determinations of molecular weight were done by sedimentation and diffusion. Molecular weights obtained by this method do not depend on assumptions about the molecular configuration. Light scattering has been used extensively for the determination of particle weight. The method is particularly useful because of its sensitivity over a wide range of particle sizes and its ability to provide information on particle shape. Subsequent studies have established the correctness of the assumption that water is released upon polymerization. TMV, a protein seems to be a trimer of the chemical subunit. Its polymerization has been studied primarily by light scattering and osmotic pressure methods. Within certain limits, the polymerization can be interpreted quite accurately in terms of the mathematics of condensation polymerization. Accompanying the release of water molecules upon polymerization is an increase in partial specific volume. Hydrogen ions are bound during polymerization.