STUDY OF CONFORMATIONAL TRANSITIONS IN POLY(A) BY THE BUFFER CAPACITYTECHNIQUE

Proton buffer capacity plots for poly(A) are obtained and expanded in basis functions corresponding to ionization of groups of various types . It is found that these curves have three sharp peaks: two neighborin g peaks at the pH range in which the coil to double helix transition o f poly(A) occurs, and a third peak at lower pH. The first two peaks ar e assigned to formation of B and A forms. It is shown that the A form of poly(A) is produced in two stages, of which the first is a highly c ooperative process. The third peak may correspond to a conformational change in the B form of poly(A). A diagram of distribution of differen t forms of poly(A) as dependent on pH is presented. On the basis of th e literature data, the pK values of three conformational transitions i n poly(A) at various ionic strengths and temperatures are computed.