Periodate oxidation histochemical oxidations

Histochemical demonstration of most of the O-acetylated sialic acids is possible because substituents on the side chain of Neu hinder periodate oxidation of this part of the molecule to an extent dependent on the number and position of the O-acetyl groups already mentioned. Correspondingly, removal of these ester groups by alkaline treatment (0.5% KOH in 70% ethanol91) may increase the staining reaction of a sialic acid. For example, the presence of O-acylated sialic acids has been demonstrated in colonic, epithelial mucin of man and various mammals (summarized in Ref. 91), in healthy and diseased, human small-intestine,188-190 in bovine submandibular gland,182 in mouse and rat erythrocyte-membranes,191 and in human lymphocytes.192... 

D. Volz, P. E. Reid, C. M. Park, D. A. Owen, and W. L. Dunn, Histochemical procedures for the simultaneous visualization of neutral sugars and either sialic acid and its side chain O-acyl variants or O-sulfate ester. I. Methods based upon the selective periodate oxidation of sialic acids, Histochem. J., 19 (1987) 249-256 Histochemical procedures for the simultaneous visualization of neutral sugars and either sialic acid and its O-acyl variants or O-sulfate ester. II. Methods based upon the periodic acid-phenylhydrazine-Schiff reaction, Histochem. J., 19 (1987) 257-263. 

The chemistry and analysis of sialic acids have been reviewed. Picomole quantities of sialic acids have been measured by the fluorescence produced by the periodate-oxidized acid in the thiobarbituric acid reaction. " Contamination of the sialic acids with 2-deoxy-D-eryt/iro-pentose (derived from cellular material) could be detected by a downfield shift of the excitation maximum. Fluorescent derivatives are also produced when free sialic acids react with pyridoxamine, a procedure that compares favourably with the thiobarbituric acid reaction for determining sialic acids. Keto-acids e.g. pyruvic acid) interfere with the determination, but 2-deoxy-D-arabmo-hexose and 2-deoxy-D-c/-ytliro-pentose do not. A nonfading chromophore is produced when DMSO is used instead of n-butanol in the thiobarbituric acid ssay for sialic acids. A new histochemical method for the visualization and identification of unmodified or 0-acylated sialic acids has been reported. ... 

Periodate in aqueous perchloric acid oxidizes the glycuronic acid residues of glycosaminoglycuronans with sufficient selectivity that the reagent has been proposed for histochemical classification. Several other histochemical applications of periodate for the detection of carbohydrates and sialic acids specifically,have been described. 

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