Thiolation for labeling of proteins, using catalysis by silver and imidazole combined

Abstract

1. 1.|Compounds containing primary amino groups could be thiolated rapidly at pH 7.5–8 by N-acetylhomocysteine thiolactone with catalysis by Ag + and imidazole present together. 2. 2.|Using equimolar thiolactone and Ag + the characteristics of these reagent mixtures at varying ratios of imidazole were investigated. Suggestions are made as to the species present in the course of these reactions. 3. 3.|Hydrolysis of the thiolactone competed with aminolysis and limited acylation of amino compounds. The extent of acylation was measured on glycine and was improved by increasing the concentration of Ag + and thiolactone (equimolar) but not by increasing the relative imidazole content, which somewhat increased the rates. 4. 4.|Rabbit γ-globulin was extensively thiolated using 0.3 M Ag + and thiolactone, with 2 and with 8 equiv of imidazole. For comparison, globulin thiolated with catalysis by imidazole alone was also extensively (although slowly) acylated but lost many of the thiol groups in the absence of the protecting Ag +. 5. 5.|A procedure for protein thiolations is given, and factors governing the choice of the reagent mixtures are discussed.