The Thiobarbituric Acid Assay of Sialic Acids

Publisher Summary This chapter discusses the different aspects of thiobarbituric acid assay of sialic acid. Periodate oxidation of the neuraminic acid backbone of sialic acids results in the formation of β -formylpyruvic acid from carbon atoms 1 to 4. The N -acetyl or N -glycolyl group of sialic acids apparently does not interfere with periodate oxidation. β -Formylpyruvic acid is coupled with 2-thiobarbituric acid to form a red chromophore with a maximum absorption at 549 mμ. It is found that as only free sialic acids are reactive in the assay, hydrolysis of sialic acid-containing material must be carried out for the measurement of total sialic acids. The assay is suitable for measuring the release of bound sialic acid by sialidase. A series of 2-keto, 3-deoxy sugar acids, found in bacteria, also react in the thiobarbituric acid assay. These produce a chromogen with a peak at 549 mμ. They can be readily distinguished from sialic acids because they are not reactive in the orcinol or direct Ehrlich assays for sialic acids. The hydrolysis frees all the sialic acids from several mucoproteins that have been tested except for brain tissue where release of sialic acids takes place for several hours.