SOME EFFECTS OF IODINE AND OTHER REAGENTS ON THE STRUCTURE AND ACTIVITY OF TOBACCO MOSAIC VIRUS

Area of Science:

• Biochemistry
• Virology
• Molecular Biology

Background:

• Tobacco mosaic virus (TMV) is a well-studied plant virus.
• Understanding the role of specific chemical groups in viral infectivity is crucial for virology.

Purpose of the Study:

• To investigate the role of sulfhydryl (SH) groups in the biological activity of tobacco mosaic virus.
• To determine the effects of chemical modification on TMV infectivity and structure.

Main Methods:

• Quantification of SH groups in denatured TMV using titration methods (ferricyanide, tetrathionate, p-chloromercuribenzoate) and uric acid reagent.
• Chemical modification of native TMV using iodine to oxidize SH groups and potentially modify tyrosine groups.
• Assessing viral biological activity through lesion counts on Nicotiana glutinosa and disease symptoms in Turkish tobacco plants.
• Inactivation studies using iodoacetamide and p-chloromercuribenzoate.

Main Results:

• Denatured TMV contains a specific number of SH groups.
• Iodine treatment can abolish SH groups in native TMV without immediate loss of infectivity.
• TMV retains biological activity after SH group oxidation by iodine, provided tyrosine groups remain unaltered.
• Inactivated TMV (due to excessive iodine or heat affecting tyrosine) shows conversion to di-iodotyrosine.
• Iodoacetamide inactivates TMV under conditions that minimally affect SH groups, while dilute p-chloromercuribenzoate does not.

Conclusions:

• Sulfhydryl (SH) groups are not essential for the initial biological activity of tobacco mosaic virus.
• Tyrosine group modification is critical for TMV inactivation by iodine.
• The mechanism of TMV inactivation involves specific chemical alterations to the virus structure.