Quantitative Problems in Sialic Acid Release

A number of problems arise when sialic acids are to be released prior to quantitative analysis, in general by sialidase digestion or mild acid hydrolysis, as described in chapter C. 

Sialidase digestion frequently leads to incomplete release of sialic acid, thus giving false values for total contents in sialoglycoconjugates. The reasons for the incomplete release are often linked with the nature of the substance as has been discussed in section I. 

Mild acid hydrolysis is less specific than sialidase digestion and also less expensive. Attention should be paid to the different conditions of hydrolysis required for various glycoconjugates and the slower release of 0-acylated sialic acids relative to Neu5Ac (Ledeen and Yu 1976) (see chapter C). To obtain optimal quantitation, a release curve for sialic acid should be prepared (Schauer et al 1975, O Kennedy 1979). In addition to this precaution, the destruction of sialic acid under the conditions of the hydrolysis should be assessed (e.g. Schauer et al 1975, O Kennedy 1979). The inclusion of a sialic acid standard under the conditions of hydrolysis will allow assessment of the level of destruction (Schauer et al 1975, Schauer 1978, Caimi et al 1979). 

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