Methylation or lactonization of acid mucins by acid methanolic reagents in histochemistry

With the demonstration that cationic dye staining of acid mucins can be prevented by treatment with hydrocholoric acid or thionyl chloride in nonpolar, nonalcoholic solvents it has been contended that the blockade has occurred by lactonization of the acid mucosaccharides. It is further contended that also in methanolic HCl lactonization is the only process by which cationic dye staining of acid mucins occurs to the exclusion of methyl esterification of the carboxyls. We have demonstrated that an acetylation adequate to prevent the PAS reaction of mucins does not prevent either direct cationic dye staining or its blockade by methylation, and that periodic acid cleavage of the 2,3 glycol of hyaluronic acid mucins does not prevent methylation blockade of cationic dye staining. With occupying or destroying the variation of(3) hydroxyl on which variation of-lactonization would have to occur it is believed that the successful blockade must have occurred by methyl esterification of the carboxyl. Lactonization must be regarded as an alternative rather than an exclusive pathway for this blockade.