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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 (ΔGD), 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 (µU) indicated urea uptake throughout the pH range examined, with values of µU 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 ΔGD, ΔV and µU. 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)

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