Stereochemistry of the Active Site of α-Chymotrypsin: THE BINDING GEOMETRY OF TRYPTOPHAN DERIVATIVES

Abstract

Abstract Chymotrypsin (EC 3.4.4.5) hydrolyzes methyl dl-1,2-dihydronaphtho[2,1-b]furancarboxylate (IV) very rapidly and with high d specificity. The isomeric methyl dl-dihydronaphtho[1,2-b]- and -[2,3-b]furan-2-carboxylates are much poorer substrates than IV, and are hydrolyzed with less stereospecificity. The binding site has been mapped to identify areas displaying steric hindrance to binding and areas of a polar and nonpolar nature. The results confirm Niemann's hypothesis that the aromatic binding site in chymotrypsin is approximately planar, elongated, and curved. Methyl N-acetyl-l-3-(1-naphthyl)alaninate (VII) was also found to be a very good substrate, in contrast to its 2-naphthyl analogue, which is about 100 times less reactive than VII. A likely conformation of methyl N-acetyl-l-tryptophanate during hydrolysis at the active site of chymotrypsin is proposed.