An Isomorphous Heavy Atom Substitution at the Active Site of Gamma-chymotrypsin.

The author would like to express his appreciation to Professor Ephraim Katchalski for his hospitality, to Professor Michael Sela for samples from his collection and for valuable discussion, to Professor Franz Sondheimer for the use of a spectrophotometer, and to Dr. Israel Schechter and Mr. Shmuel Shaltiel for valuable advice. Abbreviations used are: pTR, poly-L-tyrosyl ribonuclease; pApTR-L, lightly alanylated pTR, i.e., poly-DLalanyl-poly-L-tyrosyl ribonuclease; pApTR-H, heavily alanylated pTR; A(T,G)L, polv-DL-alanyl-poly(L-tyrosyl, L-glutamyl)-poly-L-lysine; (T,G)A-L, poly-(Ltyrosyl, L-glutamyl)-poly-DL-alanyl-poly-L-lysine; R, ribonuclease; pAR, poly-DL-alanyl ribonuclease; and pTpAR, poly-Ltyrosyl-poly-DL-alanyl ribonuclease.