FIGURE 2.1 Alkylation of nucleophiles. A comparison of the reaction of two alkylating agents with cysteine. The data are taken from Dahl, K.H. and McKinley-McKee, J.S., The reactivity of afnity labels. A kinetic study of the reaction of alkyl halides with thiolate anions-A model reaction for protein alkylation, Bioorg. Chem. 10, 329-341, 1981. The data shown is the estimated pH-independent rate constants at 37°C. Also shown is the reaction of acetyl chloride with the sulfhydryl group of cysteine to yield an unstable thioester derivative.