Association-Dissociation Phenomena in Biopolymers

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Abstract
Association between biological macromolecules by non-covalent interactions is not only a wide-spread phenomenon in nature but also is of invaluable importance for life processes. In most cases the association is practically irreversible under experimentally accessible conditions, but a few examples are known where a reversible association-dissociation equilibrium can be studied. Such studies are of basic importance for the understanding of the association mechanisms and thus for the questions concerning the self-organization of living material. In addition, association-dissociation equilibria also must be assumed to play an important part in the regulative systems of the organisms. Very little data is available for the parameters of the micro-environment of the biological macromolecules in the different cell compartments, so that in vitro studies of regulative processes under a wide variety of solvent conditions are not only of academic interest. In the present review some examples of association-dissociation equilibria involving, e.g., chymotrypsin, chymotrypsinogen, glutamate dehydrogenase, hemerythrin, hemocyanins, phosphofructokinase, phosphorylase, tobacco mosaic virus protein, are compiled which are among the most thoroughly studied and which are considered to be typical representatives of the different aspects of this phenomenon. Both regulative and probably non-regulative associations are discussed. Closed equilibria serving as models for self-assembly of concrete structures, as well as open equilibria showing possibilities of looser but wide-ranging organizations are presented. Association between identical subunits is compared to that between different components, especially between proteins and nucleic acids, e.g., tRNA and aminoacyl tRNA synthetase, represser and DNA. The physico-chemical data which are known up to now are presented and the physiological aspects are discussed.