Positive periodic acid-Schiff staining of acid mucopolysaccharides

Evidence is presented to demonstrate that acid mucopolysaccharides will stain with the periodic acid-Schiff technique following prolonged oxidation with periodic acid. Smears of purified acid mucopolysaccharides begin to stain slightly with the Schiff reagent after 4 hr of periodate oxidation and reach an optimal staining intensity some time between 7 and 16 hr. The acid mucopolysaccharides in umbilical cord and cock's comb sections begin to stain at about 7 hr, reaching an optimum between 16 and 24 hr. It is suggested that the mechanism of staining of acid mucopolysaccharides in the PAS technique appears to derive from cleavage oftrans groups of the hexuronic acid fraction which require prolonged oxidation since the theoretical more yield is reached with difficulty. Moreover, it would appear that the mechanism of staining with glycogen under the usual conditions of PAS staining perhaps derives from end-group oxidation and subsequent Schiff staining of the engendered aldehydes since glycogen is almost entirely in thetrans configuration. Acid mucopolysaccharides, on the other hand, will not stain uncer the usual conditions as they appear to have a negligible proportion of end groups.