Investigation of the inhibition of leukotriene A4 hydrolase.

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 A4 (LTA4) hydrolase (EC 3.3.2.6), we prepared a number of derivatives of 1-L and other related structures, and assayed their inhibition of LTA4 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 LTA4 binding modes in the active site of LTA4 hydrolase, including a possible direct role for the carboxylic acid of LTA4 in the enzyme-catalyzed hydrolysis of leukotriene A4, are discussed.