Metabolism of 4O-Methyl-N-acetylneuraminic Acid a Synthetic Sialic Acid.

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    • Abstract:
      4-O-Methyl-N-acetylneuraminic acid shows a strong positive periodate-thiobarbiturate reaction. The mechanism of dye fromation in this test for sialic acids is discussed in view of the studies already published. An efficient preparation of a tritium-labelled 4-O-methylneuramic acid, with high specific radioactivity, by an oxymercuration-demecuration procedure is presnted. Sialyltransferase 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 substances. 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. Theisolated 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 dislplays a marked resistance to desialytion by Vibro chlorae neuraminidase. 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. The influence of substitution at C-4 of neuraminc acid on the enzymatic reaction mechanisms is discussed. [ABSTRACT FROM AUTHOR]
    • Abstract:
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