Investigation of the inhibition of leukotriene A 4 hydrolase

Abstract

In an effort to better understand the favorable binding interactions between the reversible picomolar inhibitor 3-(4-benzyloxyphenyl)-2-( R)-amino-1-propanethiol ( 1) and leukotriene A 4 (LTA 4) hydrolase (EC 3.3.2.6), we prepared a number of derivatives of 1- l and other related structures, and assayed their inhibition of LTA 4 hydrolase-catalyzed hydrolysis of l- alanine-p- nitroanilide . The inhibition data was analyzed using a weighted non-linear least-squares curve fitting computer program developed for this purpose to fit data derived under the non-Michaelis-Menten condition of [I] t < [E] t. The free thiol is necessary for sub-micromolar binding and the enzyme prefers the R enantiomer over the S enantiomer, in contrast to the stereoselectivity displayed towards bestatin, an inhibitor of somewhat similar structure. Substitution of acid moieties around the periphery of the benzyloxyphenyl portion of 1- l leads to substantially decreased binding, suggesting that this group resides within a large hydrophobic pocket when bound to the enzyme. Possible LTA 4 binding modes in the active site of LTA 4 hydrolase, including a possible direct role for the carboxylic acid of LTA 4 in the enzyme-catalyzed hydrolysis of leukotriene A 4, are discussed.