ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Thermodynamic analysis of proton- and urea-induced dissociation of tobacco mosaic virus: stoichiometry, common ion effect, cooperativity, heterogeneity of subunits and the effect of urea as a homogenizer

C. F. S. Bonafe, D. F. L. Neto, E. A. Martínez, A. L. Carvalho, and J. A. C. Bispo

Departamento de Bioquímica e Biologia Tecidual, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil

E-mail: jose.a.c.bispo@gmail.com

Received: 16 December 2019  Accepted: 28 February 2020

Abstract:

The urea- and pressure-induced dissociation of tobacco mosaic virus (TMV) and proton involvement were investigated using a thermodynamic approach that considered the extent of reaction for protons and urea. The stoichiometry of these effectors was determined, as were the Gibbs free energy of dissociation (ΔG_D), the volume change associated with dissociation (ΔV) and the Hill coefficient (H). At low pressure, the proton release ((mu_{{H^{ + } }})) was 1.9 and 1.4 mol H⁺/mol of TMV at pH 4.8 and 6.8, respectively. Below pH 4.5 and at pH 6.2, there was proton absorption ((mu_{{H^{ + } }}) < 0). The urea stoichiometry at atmospheric pressure (µ_U) indicated urea uptake throughout the pH range examined, with values of µ_U from − 1.8 to − 2.2 mol U/mol of TMV subunit at a urea concentration (expressed in pU) of − 0.18 and − 0.55, respectively. The presence of urea resulted in a much smoother dissociation profile, as indicated by the values for ΔG_D, ΔV and µ_U. This finding suggested an important role for urea in promoting homogenization, as previously reported in the literature. Overall, compared to available methods, the thermodynamic procedure described here allowed a much more detailed analysis of the thermodynamic parameters involved and the detection of properties associated with homogenization by urea.

Keywords: Cooperativity; Ion effect; Proton and urea effect; Stoichiometry of effectors; Tobacco mosaic virus; Urea homogenization

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01125-1

Chemical Papers 74 (9) 2861–2874 (2020)