STUDY OF A SULFONYL DERIVATIVE OF ALPHA-CHYMOTRYPSIN BY CHLORINE NUCLEAR MAGNETIC RESONANCE

The width of the 35Cl nuclear magnetic resonance line provides a measure of the rotational motion of the inhibitor, p-mercuribenzenesulfonyl fluoride (RHgCl), attached to the active site of α-chymotrypsin in aqueous NaCl solution. The inhibitor appears to bind to the active serine at the catalytic site. If a single methionine residue on the enzyme is first alkylated with benzyl bromide, subsequent binding of RHgCl is still specific for the active site, but the observed 35Cl resonance line is broadened relative to the inhibited native enzyme. This indicates a more restricted rotational motion of the inhibitor attached to the S-benzylmethionine-chymotrypsin. In 8 M urea, however, the line width for RHgCl attached to S-benzylmethionine-chymotrypsin is the same as for RHgCl attached to native Chymotrypsin. Apparently a well-defined secondary and tertiary structure at the active region is necessary for the alkyl group to affect motion of the inhibitor at the active site. © 1968, American Chemical Society. All rights reserved.