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pubmed:abstractText |
1. Sheep colonic mucin contains three types of sialic acids, separable from the macrostructure by mild acidic hydrolysis. These are composed chiefly of N-acetyl-and N-glycollyl-neuraminic acid in ratios between 1:1.2 and 1:3.5 for different preparations of the mucin. The third sialic acid appears to be a diacetylated neuraminic acid. 2. A particle-free enzyme preparation, obtained from sheep colonic mucosa by gentle homogenization and high-speed centrifugation, catalyses a series of reactions involving N-acylamino sugars and leading to the formation of sialic acids in vitro: (i) phosphorylation by ATP of d-glucosamine, N-acetyl-and N-glycollyl-d-glucosamine; (ii) conversion of N-acetylglucosamine 6-phosphate into N-acetyl-d-glucosamine 1-phosphate; (iii) formation of sialic acids from phosphoenolpyruvate and N-acetyl- or N-glycollyl-d-glucosamine; (iv) formation of N-acetylneuraminic acid from uridine diphospho-N-acetylglucosamine or from N-acetylmannosamine; (v) incorporation of l-[U-(14)C]serine into the mucin by whole mucosal preparations.
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