Tobacco mosaic virus molecular weight

High molecular weight mesophases were first studied during the late 1930 s using suspensions of tobacco mosaic virus (TMV). Bawden and Pirie (26) reported a solution of TMV separated into two phases as the concentration was increased, one of which was birefringent. 

Regarding the mass range, DNA ions of 108 Da were weighed by mass spectrometry [77], In the same way, non-covalent complexes with molecular weights up to 2.2 MDa were measured by mass spectrometry [78], Intact viral particles of tobacco mosaic virus with a theoretical molecular weight of 40.5 MDa were analysed with an electrospray ionization charge detection time-of-flight mass spectrometer [6]. 

Fig. 12. Mass spectra of Rice Yellow Mottle Virus (RYMV) and Tobacco Mosaic Virus (TMV) particles analyzed with an electrospray ionization charge detection time-of-flight mass spectrometer. Inset, electron micrographs of the icosahedral RYMV (diameter 28.8 nm) and the cylindrical TMV (-300 nm long and 17 nm in diameter). The known molecular weight of RYMV and TMV are 6.5X106 and 40.5X106 Daltons,respectively...

The exponent a in the intrinsic viscosity-molecular weight relationship ([rj] = K.M ) of a polymer is associated with the expansion of the polymer in solution, and hence with the conformation and stiffness of the polymer (Table 24). The a values of tobacco mosaic virus, Kevlar and helical poly(a-amino acids) are close to 2, which means that they take rigid-rod structures. The a values of vinyl polymers are usually 0.5-0.8, indicating randomly coiled structures. In contrast, the a values of substituted polyacetylenes are all about unity. This result indicates that these polymers are taking more expanded conformations than do vinyl polymers. This is atrributed to their polymer-chain stiffness stemming from both the alternating double bonds and the presence of bulky substituents. 

Mesophases containing high molecular weight components have been known for many years. The earliest studied involved polyelectrolytes such as tobacco mosaic virus (1). Approximately 30 years ago mesophases were observed... 

Some colloids consist of well-defined molecules, with constant molecular weight and definite molecular shape, permitting them to be piled in a crystalline array. Crystalline proteins include egg albumin (MW 43000) and hemoglobin (MW 68000). Even viruses, such as, tobacco-mosaic virus, have been crystallized their molecular weights are in the neighborhood of 10,000,000 (bushy-stunt virus) to 2,000,-000,000 (vaccinia virus). 

Figure 4. Flory-Mandelkern correlation of intrinsic viscosity, molecular weight, and translational diffusion coefficient for a variety of polymer solvent systems, demonstrating the insensitivity of these data to the structure of the macromolecule ( X PS/tetrahydrofuran (37) (O), protein random coils in 6M guanidine hydrochloride-0,IM mercaptoethanol (26) (X), tobacco mosaic virus in aqueous solution (11) ( ), bovine serum albumen in aqueous solution (37).

Sumner s analytical studies convinced him that urease was a protein. This conclusion was resisted by the chemical community but John H. Northrop s (1891-1987) crystallization of pepsin in 1930 at the Rockefeller Institute in New York City and its unambiguous decomposition into amino acids fully vindicated Sumner. Sumner and Northrop were able to make use of the ultracentrifiige developed by Svedberg and the electrophoresis technique developed by his student Tiselius to fully establish purities and molecular weights of their enzymes. Sumner and his coworkers then crystallized trypsin and chymotrypsin. Sumner and Northrop shared the 1946 Nobel Prize in chemistry with Wendell M. Stanley (1904—71), who in 1935 crystallized the tobacco mosaic virus in his laboratory at the Rockefeller Institute. 

Quaternary structure designates the association of several subunits (individual polypeptide chains) to form the whole (intact) molecule. Hemoglobin, for example, is constructed of two identical A and two identical B chains. On the other hand, tobacco mosaic virus is composed of, depending upon conditions, 2100 polypeptide chains. The molecular weights of the individual peptide chains are relatively low, varying between about 1600 and 100,000. 

A somewhat different type of mechanism is employed by Tobacco Mosaic Virus for the expression of the coat protein gene which is situated towards the 3 end of the virion ENA and is not expressed when intact virion RNA is translated in vitro. In infected plants, a low molecular weight ENA coding for the coat protein is produced, either by selective transcription or by selective processing of the viral genome (87). 

The purified preparations from most sources are not homogeneous even the RNA of tobacco mosaic virus is polydisperse, although this may be a reflection of association and disassociation of similar particles. Molecular weights of RNA are estimated between 10,000 and 600,000. RNA preparations from various sources contain variable ratios of bases. The relative amounts of purines usually exceed the pyrimidines by a small factor and guanine and cytosine tend to exceed adenine and uracil, respectively. These differences are well established, and force the abandonment of the old concept of a regular tetranucleotide structure. It is not known how many specific types of RNA molecules may be formed in a given cell, but it appears that RNA can be fractionated into components with different ratios of bases, and there is no reason to believe that further separations will not be accomplished. 

High molecular weight ribonucleic acids of exceptional purity have been prepared from certain viruses. The RNA of the tobacco mosaic virus, for example, has a molecular weight of 2 million. 

Each tobacco mosaic virus particle consists of one long thread of nucleic acid embedded in protein. The protein surrounds the nucleic acid in loops or in the fashion of screw threads making up the super-molecule. Treatment with phenol separates nucleic acids from protein. The nucleic acid obtained in this mild way remains infectious, and in a host cell can cause virus multiplication and consequent symptoms of disease. About 95% of the material is protein it consists of individual subunits with a molecular weight of 17,500, which exhibit a marked tendency to aggregate At neutral or slightly acidic pH the protein molecules aggregiite to little rozls, very similar to the intact virus particles both in shape and size. The amino acid sequence is now known. Mutants obtained by nitrous acid treatment (see above) show up differences in the amino acid sequence usually only one amino acid has been replaced, for example, serine by leucine, or leucine by phenylalanine. 

Tobacco mosaic virus has been shown by electron microscopy to be shaped like a cylinder 150 A in diameter and 3,000 A long. Its molecular weight is about 40 million, and its partial specific volume is 0.73 cm /g. Estimate the diffusion coefficient of this... 

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