Metabolism of 4-O-methyl-N-acetylneuraminic acid a synthetic sialic acid.
1. 4-O-Methyl-N-acetylneuraminic acid shows a strong positive periodate-thiobarbiturate reaction. The mechanism of dye formation in this test for sialic acids is discussed in view of the studies already published. 2. An efficient preparation of a tritium-labelled 4-O-methyl-N-acetylneuraminic acid, with high specific radioactivity, by an oxymercuration-demercuration procedure is presented. 3. Sialytransferase activities in microsomal fractions of equine liver using desialylated fetuin are studied. The enzyme activity, assayed in a radioactive procedure, shows an apparent Km value for CMP-N-acetylneuraminic acid of 0.7 mM, whereas this value is 3.4 mM for CMP-4-O-methyl-N-acetylneuraminic acid. Differences are also observed in the maximal velocity for the two substrates. 4. The equine liver system can be used to prepare substantial amounts of fetuin containing radioactive N-acetylneuraminic acid or 4-O-methyl-N-acetylneuraminic acid. The isolated reaction products show similar sialic acid release by treatments with acid or fowl-plague virus neuraminidase. In contrast, 4-O-methyl-N-acetylneuraminic acid-fetuin displays a marked resistance to desialylation by Vibrio cholerae neuraminidase. 5. Free 4-O-methyl-N-acetylneuraminic acid is completely resistant to the action of acylneuraminate pyruvate-lyase. It does not inhibit the enzymic cleavage reaction of N-acetylneuraminic acid. 6. The influence of a substitution at C-4 neuraminic acid on the enzymatic reaction mechanisms is discussed.
D000818:Animals; D003124:Colorimetry; D006736:Horses; D009439:Neuraminidase / Q000494:pharmacology; D007652:Oxo-Acid-Lyases / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism*; D012799:Sialyltransferases / Q000378:metabolism; D000509:alpha-Fetoproteins / Q000378:metabolism
D012794:Sialic Acids; D000509:alpha-Fetoproteins; C026321:4-O-methyl-N-acetylneuraminic acid; D012799:Sialyltransferases; D009439:Neuraminidase; D007652:Oxo-Acid-Lyases; C018728:N-acetylneuraminate lyase