Effects of Self-Interaction of Ligands on Binding Processes: Studies with the Acceptors Firefly Luciferase and Thyroglobulin

Abstract

Previously presented binding theory (Nichol, Smith, and Ogston 1969), describing the effects of ligand self-interaction on binding processes, is applied to the description of two experimental systems, of different type. First, the theory is used to re-examine the sigmoidal kinetic results obtained by other workers (Denburg and DeLuca 1968) with the enzyme firefly luciferase. Denburg and DeLuca attributed the pseudo-allosteric behaviour of the enzyme to the reversible dissociation of the substrate: the present treatment supports the general conclusions drawn by these workers, but considers both substrate self-interaction and binding of the substrate to the enzyme. Secondly, the theory is used to describe the binding of the dimerizing thyroid acid proteinase to its natural substrate, thyroglobulin. In this case the enzyme is regarded as the ligand. It is suggested that this approach may prove useful in describing the binding of other self-associating enzymes to their macromolecular substrates.