A simple method for the determination of the O-acetyl substitution pattern of the sialic acids of colonic epithelial glycoprotein

Abstract

A simple, rapid scheme is described for the quantitative division of the sialic acids of a glycoprotein into four classes: (a) those bearing no O-acyl substituents, (b) those with an O-acyl substituent at position C7, (c) those substituted at C9, and (d) those substituted at C8 or which are either di-(C7C8, C7C9, C8C9) or tri-(C7C8C9) substituted. This scheme can be applied to samples containing as little as 230 μg of sialic acid and requires neither acid hydrolysis nor expensive instrumentation. In combination with previously published techniques it is possible to estimate: (a) the side-chain substitution pattern of those sialic acids which are Vibrio Cholera neuraminidase (EC 3.2.1.18) insensitive, (b) the percentage of sialic acids which are Vibrio Cholera neuraminidase insensitive because of an ester substituent at either position C4 or C1, and (c) the percentage of those sialic acids which bear more than one side-chain substituent.The application of this procedure to epithelial glycoproteins isolated from the colons of man and rat and to a commercial sample of bovine submaxillary mucin is described. Evidence is presented which suggests that either these glycoproteins contain little or no C9-O-acetyl sialic acids and (or) that, under the conditions used, such acids are oxidized to completion.