Calorimetric Studies of Biopolymers and Aggregates of Phospholipids

Abstract

The structural transformations that biopolymers undergo in aqueous solution are complex processes, whose mechanisms can only be explained by the coupling of various partial processes. A spectroscopic analysis of the states of the system often requires considerable effort. In many cases, calorimetric studies have proven to be sufficient for a general characterization of the behavior of the system. These measurements provide information on the stability of the initial state and on the cooperativity of the total process. From the thermodynamic parameters of the system, knowledge on the structure-determining influence of the various types of interand intramolecular interactions is obtained. This not only applies to solutions of biopolymers and analogous model substances, but also to solutions of biopolymer complexes with lowmolecular-weight ligands and to aqueous suspensions of self-aggregating phospholipids. Possibilities and limitations of the calorimetric methods of measurement are demonstrated for typical examples from the numerous polypeptide and polynucleotide systems and the phospholipid bilayer systems that have been studied. In addition, the special problems involved in carrying out measurements on dilute solutions are pointed out. Here, the latest advances made in measuring techniques are readily apparent.

Thermodynamics of double- and triple-helical aggregates formed by self-complementary oligoribonucleotides of the type rAxUy

“…However, oligoribonucleotides with a high content of AU base pairs actually do not melt in a two-state manner (Breslauer et ah, 1975). Therefore, a more careful analysis of thermal denaturation processes of oligoribonucleotides like rAxU^, needs model-independent data which can be obtained from calorimetric measurements (Breslauer, 1986; Marky & Breslauer, 1987;Sturtevant, 1987;Ackermann, 1989).…”