Histochemical studies of the mechanism of the periodic acid-phenylhydrazine-Schiff (PAPS) procedure.

Histochemical investigations of the periodic acid-phenylhydrazine-Schiff (PAPS) procedure were carried out on tissues containing carbohydrate macromolecules known to produce on periodate oxidation, only sialic acid monoaldehydes or hexosedialdehydes or mixtures of the two. The results indicated that the PAPS reaction is a generalized phenomenon independent of the hydrazine or hydrazide used, the nature of the Schiff reagent or the presence of anionic groups. It is proposed that phenylhydrazine condenses with periodate-engendered sialic acid monoaldehydes to yield the corresponding phenylhydrazone and with periodate-engendered dialdehydes to yield the corresponding morpholine or azido derivatives. Subsequent Schiff treatment results in the reversal of the blockade of sialic acid monoaldehydes but not of the dialdehydes, thus leading to selective Schiff staining of sialic acid residues.