The histochemical properties of some periodate‐reactive mucosubstances of the pregnant Syrian hamster before and after methylation with methanolic thionyl chloride

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Abstract
SYNOPSIS: The mucosubstances secreted in various tissues of pregnant Syrian hamsters exhibit a wide range of histochemical characteristics.When sections of fixed tissues containing these mucosubstances are treated with a methanolic solution of thionyl chloride for four hours at room temperature, nucleic acid phosphate groups, protein and sialomucin carboxyl groups, and the sulphate groups of many sulphomucins are apparently esterified. In sulphomucins believed to contain carboxyl and sulphate groups, only the sulphate is esterified; the carboxyls (uronic acid groups ?) are left free. If such methylated mucins are saponified (to remove their ester methyl groups) some, but not all, of their histochemical reactions for “free” sulphate are restored. Some desulphation, however, usually occurs during the methylation process. A few sulphated mucins, such as those in the goblet cells of the small intestine, are desulphated completely. The ability to esterify many sulphated mucins without either desulphating them completely or extracting them from the tissue distinguishes methanolic thionyl chloride from the hot methanolic solutions of hydrochloric acid usually used for methylating tissue sections. Moreover, methanolic thionyl chloride solutions are much easier to use.The little chemistry that is at present known about the reactions between methanol and thionyl chloride is insufficient to explain how methanolic thionyl chloride solutions actually methylate polyanionic substances in tissue sections.