Effect of amino acid replacement on the stability of the tobacco mosaic virus protein structure.

A comparative polarographic study on the alkaline degradation of tobacco mosaic virus (TMV) strain vulgare and its mutant TMV 483, having histidine instead of glutamine at position 9 in the polypeptide chain, was performed. In the course of alkaline degradation and subsequent incubation in the supporting electrolyte at 0 degrees C TMV 483, unlike TMV vulgare, showed a polarographic effect indicating the unfolding of the TMV polypeptide. It was concluded that the replacement of glutamine-9 by histidine causes a decrease in the stability of the three-dimensional structure of the TMV protein subunit. A polarographic study of untreated virions as well as denatured proteins of both TMV strains showed that histidine, when incorporated into the polypeptide chain, is not active polarographically at the conditions used.