A note on the estimation of microbial glycosidase activities by dinitrosalicylic acid reagent

In the estimation of glycosidase activity by dinitrosalicylic acid (DNS) re agent, the stoichiometry of DNS reduction was reported to increase proporti onately with the increase in the number of glycosidic linkages present in o ligosaccharides liberated by the enzyme. The relationship between increases in DNS reduction and increases in the number of glycosidic bonds was found to be represented by a part of a rectangular hyperbola. The increase was o ptimum with disaccharide and insignificant when the degree of polymerizatio n (DP) was greater than or equal to 10. The difference did not arise as a r esult of the DNSA discriminating between mono- and oligosaccharide oxidatio n. The relationship stemmed from the acidity of the hydroxyl group adjacent to the reducing group, which repressed DNS reduction. The acidity is likel y to decrease with an increase in oligosaccharide chain length. It is sugge sted that DNS reduction is actually optimum and uniform for all oligosaccha rides of DP greater than or equal to 10 and that it is minimum for monosacc haride. Thus the introduction of rectification factors in the estimation of glycosidase activities by the DNS method appears to be justified.