INVESTIGATION OF THE INHIBITION OF LEUKOTRIENE A(4) 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 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.