The emission, excitation and polarization spectra of tobacco mosaic virus protein were identical for the aggregated protein and disaggregated protein (A Protein) with the exception that the quantum yield of fluorescence decreased 25% on aggregation. This decrease in the absence of other spectral changes suggests a quenching interaction between adjacent subunits. The aggregation apparently produces, at most, minor conformational changes within subunits. The polarization of fluorescence is low but does not decrease on aggregation, indicating that energy migrates efficiently within subunits but not between subunits. Intersubunit space must be large, relative to intrasubunit space. Fluorescence from the tyrosine residues in tobacco mosaic virus protein is not observable, and evidence from the excitation spectrum of tobacco mosaic virus protein is given which suggests that tyrosine energy is efficiently transferred to the tryptophans in tobacco mosaic virus protein. These results and the low polarization indicate that tobacco mosaic virus protein subunits are rather compact. 2-p-Toluidinylnaphthalene-6-sulfonate (TNS), a hydrophobic probe, bound more strongly to aggregated protein than to A Protein. This was shown to be due to the charge change associated with the aggregation as TNS sulfonamide (TNSA) a neutral probe, was bound with equal efficiency to A Protein and aggregated protein. As exposure of the intersubunit regions led to no increase in hydrophobic binding of TNS or TNSA, the hydrophobicity of the intersubunit surface is weak.
ASJC Scopus subject areas