Nature and biosynthesis of sialic acids in the starfish Asterias rubens. Identification of sialo-oligomers and detection of [formula omitted]: N-acylneuraminate 8- O-methyltransferase and CMP- N-acetylneuraminate monooxygenase activities

Abstract

Mass spectrometric and NMR spectroscopic analyses of bound sialic acids from the starfish Asterias rubens revealed the presence of N-acetylneuraminic acid (4%), N-acetyl-8- O-methylneuraminic acid (12%), N-acetyl-9- O-methylneuraminic acid (< 1%), N-glycoloylneuraminic acid (19%), N-glycoloyl-8- O-methylneuraminic acid (47%), and N-glycoloyl-9- O-acetyl-8- O-methylneuraminic acid (18%). Analysis of sialo-oligomeric material, obtained after mild acid hydrolysis, demonstrated that N-glycoloyl-8- O-methylneuraminic acid can occur as di- and tri-oligomers, linked through the anomeric center and the N-glycoloyl moiety, Neu5Gc8Me- α(2→O5)-Neu5Gc8Me and Neu5Gc8Me- α(2→O5)-Neu5Gc8Me- α(2→O5)-Neu5Gc8Me. Studies on the biosynthesis of N-acyl-8- O-methylneuraminic acid in A rubens, using the tracer S- adenosyl- l-[ methyl- 14 C] methionine , showed that N-acylneuraminate8- O-methyltransferase activity was present predominantly in the membrane fraction. CMP- N-acetylneuraminic acid monooxygenase activity was found in the soluble protein fraction, in agreement with investigations on the corresponding vertebrate enzyme.