CARBOXYMETHYLATION OF CRYSTALLINE RIBONUCLEASE

Crystals of ribonuclease A were treated with bromoacetic acid at pH 5.5 in 75% 2-methyl-2,4-pentanediol and the products compared with those of carboxymethylation of ribonuclease dissolved in water. 1 -Carboxymethylhistidine-119-ribonuclease and 3-carboxymethylhistidine- 12-ribonuclease were obtained in a ratio of 60:1. Carboxymethylation in aqueous solution under comparable conditions of phosphate concentration yields these products in a ratio of 15:1. It is suggested that the alkylation site in the crystals is similar to, and perhaps identical with, that of at least one conformation in solution. 1 -Carboxymethylhistidine- 119-ribonuclease and 3-carboxymethylhistidine-12-ribonuclease (both prepared by reaction in aqueous solution) were crystallized, the former in the standard space group, and the latter in a different form. © 1969, American Chemical Society. All rights reserved.