THE SENSITIVITY OF THE NEURAMINOSIDIC LINKAGE IN MUCOSUBSTANCES TOWARDS ACID AND TOWARDS NEURAMINIDASE

Abstract

The decomposition of neuraminic acid by acid is accompanied by the reversible formation of a compound, probably the lactone, which renders this decomposition kinetically complex. Notwithstanding this complexity, theoretical hydrolysis curves may be obtained for the release and destruction of neuraminic acid during treatment of substances that contain it with 0.1 N acid at 80[degree]. Several such substances, notably bovine cervical mucopolysaccharide and submaxillary mucoprotein, have been examined. Large deviations from the theoretical hydrolysis curves have been observed with these two substances; two human mucopolysaccharides give slightly discrepant curves. By examining the two bovine substances after treatment with dilute acid and alkali and with the enzyme neuraminidase it is concluded that the behaviour of the submaxillary mucoprotein can be accounted for by the well-known presence of a substantial proportion of the neuraminic acid in this substance as its O-acetyl derivatives. The O-acetyl groups confer a considerable degree of neuraminidase-resistance on this material. The superficially similar discrepancies that arise in the behaviour of the bovine cervical mucopolysaccharide cannot be accounted for in this way, and it is necessary to postulate a neuraminosidic linkage in this substance which is intrinsically somewhat more stable in acid than that usually encountered. This linkage is also neuraminidase-resistant, and accounts for rather less than half of the total neuraminic acid in this substance. A consideration of the behaviour of the bovine cervical mucopolysaccharide in the N-acetylhexosamine reaction allows the tentative identification of the resistant structure as N-glycolloyl-neuraminosyl-(2 4)-N-acetylhexosamine. The other materials studied contain a rather small proportion of their neuraminic acid linked so as to be resistant to neuraminidase, and their hydrolysis curves do not seriously disagree with those predicted. The two human materials contain a somewhat larger proportion (17-25%) so linked and give slightly anomalous hydrolysis curves. The erroneous statement that bovine cervical mucopolysaccharide contains O-acetyl groups is corrected. The discrepancy between the total amount of neuraminic acid in bovine cervical mucopolysaccharide estimated in the thiobarbituric acid analysis and that shown by other methods is traced to the low colour yield of N-glycolloylneuraminic acid, as compared with the N-acetyl compound, on reaction with tniobarbituric acid.