Cyclodextrins as Enzyme Models

Abstract

Cyclodextrins are cyclic oligomers of glucose. They usually contain six, seven, or eight glucose moieties in a cyclic array. We first came upon them after we carried out a considerable amount of kinetics on the enzyme chymotrypsin and had come to the conclusion that the principal binding in the enzyme was a cyclic inclusion complex. We therefore hunted through the literature for a simple example of a cyclic inclusion complex and found that complexes of cyclodextrins had been extensively investigated.¹ So our picture of the binding exhibited by chymotrypsin (Figure l)² was mirrored by complexes shown by α, β and γ-cyclodextrins.³ (Figure 2) The cyclodextrins are not surfactants but can be considered to be simple models of surfactants in the sense that both cyclodextrins and surfactants catalyze enzymatic reactions but cyclodextrins are simpler (and smaller) than surfactants. The structure of cyclodextrins is known completely by X-ray analysis.⁴ The cyclodextrins bind small organic molecules in a stoichiometric 1:1 manner (especially in aqueous solution) and thus can be thought of as models for both surfactants and enzymes.