Abstract
The use of methyl iodide as a histochemical alkylating agent is described. Methyl iodide selectively esterifies carbohydrate and other carboxyl groups. Sulfate half esters are not affected. Phosphate esters are esterified by methyl iodide, although the latter reaction is more variable; in several tissues nuclear basophilia could not be abolished. Saponification with barium hydroxide reverses the methyl iodide blockade of basophilia. Sulfhydryl and phenol reactions are prevented by methylation with methyl iodide; amines are alkylated and the usual blockade of acidophilia by acylation or deamination is prevented. Saponification does not reverse the blockade of these latter groups. The periodic acid-Schiff and Sakaguchi reactions are not affected. Marked increases in acidophilia were noted after methylation with methyl iodide. The hypothesis that a large number of tissue acids and amines are ordinarily prevented from binding basic and acid dyes respectively by intra- or intermolecular salt linkages is set forth. Similarly, the inability of protein end groups to demonstrate chemically determined pK values (to 2.5 for carboxyl groups and to 12.0 for arginine) in their interaction with dyes is attributed to interfering salt linkages.