LACTONE FORMATION IN THE HISTOCHEMICAL EVALUATION OF ACID POLYSACHARIDES: MUCIN

The pyridine-acetic blockade of mucin metachromasia and basophilia has been ascribed to lactone formation. It is suggested that the sialic acids were particularly involved. pH data have established that carboxyl groups are required for the reaction; acetic anhydride acetylation, that hydroxyl groups are necessary. The block is reversed by alkaline hydrolysis. If alkaline hydrolysis is preceded by NH 2 (which converts lactones to amides) or LiAlH 4 (which reduces lactones to alcohols) it will no longer reverse the blockade. Other mechanisms of carboxyl blockade have been shown not to occur under the conditions of these experiments. In vitro investigations appear to support the histochemical conclusions. The implications of these experiments in regard to the configuration of sialic acid in tissue and metachromasia in general are discussed.