Inhibition of soybean lipoxygenase-1 by n-alcohols and n-alkylthiols.
A series of n-alcohols and n-alkylthiols with carbon chains from 2 to 12 were examined for the inhibition of soybean lipoxygenase-1 (L-1). The alcohol produces a competitive inhibition, the extent of which increases with an increase in the carbon number of alkyl chain up to 8. Whereas the inhibition of the alkylthiol is noncompetitive, the extent of which is almost independent from the carbon number. From the behavior of pKi dependence on the carbon number of the alcohol, the decyl group appears to be optimum to bind to L-1. The thermodynamic analysis for the inhibition based upon van 't Hoff equation indicates positive enthalpy and entropy changes for the binding of the alcohol to the enzyme and negative enthalpy and positive to negative entropy changes for that of the alkylthiol. These observations suggest that the alcohol inhibits L-1 by binding of the hydrophobic alkyl tail to the catalytic site of the enzyme by a hydrophobic interaction. The alkylthiol inhibits by binding of the nucleophilic sulfhydryl head to a polarizable region of the enzyme and the alkyl tail to a hydrophobic region of the enzyme free from the steric hindrance as an anchor.