Empirical validation of a two-state kinetic model for the B-Z transition of double-stranded poly[d(G-m(5)C)]

A formula based on a first-order kinetic equation is derived to evaluate th e rate constant of the B-Z transition of a synthetic double-stranded poly[d (G-m(5)C)] in terms of the salt concentration, the absolute temperature, an d the cooperativity index. The validity of the formula was tested using cir cular dichroism spectroscopy after variation of the type of salt (NaCl, MgC l2), the salt concentration, and the temperature of the polynucleotide solu tion. A consequence of the proposed function is that in conditions of high salt there is a predictable salt threshold which determines the particular molecular mechanism of the B-Z transition. The paper also describes the way in which this threshold level is temperature dependent. a detailed compari son of our data with the experimental data found by other authors is given. The function agrees quantitatively with the experiments and explains the c ontrasting results found in the literature about the influence in the B-Z t ransition of both the temperature and the polymer size.