Cyclodextrins to limit substrate inhibition and alter substrate selectivity displayed by enzymes

Abstract

The substrate inhibition exhibited by carboxypeptidase A in catalysing the hydrolysis of (S)-2-O-(N-benzoylglycyl)-β-phenyllactate) is limited by addition of cyclodextrins. The cyclodextrins do not significantly change the maximum rate of reaction, but they increase the concentration of the substrate at which the maximum rate of reaction is observed, by more than an order of magnitude when 0.105 mol dm⁻³ hydroxypropyl-β-cyclodextrin is used. Cyclodextrins also alter the substrate selectivity of α-chymotrypsin in catalysing the hydrolysis of (S)-N-acetylleucine methyl ester and (S)-N-acetylphenylalanine methyl ester, in favour of reaction of the former. Calculations show that these effects are due to complexation of the substrates by the cyclodextrins. Thus the results establish that cyclodextrins can be used to manipulate the concentrations of enzyme substrates in free solution in a predictable manner.