CONFORMATION OF HIGH PH FORM OF CHYMOTRYPSIN

Optical rotatory dispersion and circular dichroism spectra of chymotrypsin, its precursor, and an inhibition product have been measured. The results, together with previous information on chemical and physical properties of these proteins in solution, and on the conformation of crystalline α-chymotrypsin at neutral pH, permit some deductions about conformational features of catalytically inactive species-chymotrypsinogen and the form of chymotrypsin that predominates at high pH. The data are in agreement with the suggestion (Sigler, Blow, Matthews & Henderson, 1968) that in these forms of the protein, the carboxyl group of aspartate residue 194-which according to Blow & co-workers (Matthews, Sigler, Henderson & Blow, 1967) forms an internal ion pair with the α-amino group of isoleucine residue 16 in chymotrypsin at neutral pH-protrudes into the active site of the enzyme and thereby interferes with substrate binding. It has also been concluded that this position of the carboxyl group disrupts the bondbreaking site; this is in accord with previous studies which have indicated that in chymotrypsinogen and chymotrypsin at high pH, the bond-breaking site is unreactive. © 1969.