Species: Rattus norvegicus
Subunit composition of N-acetylneuraminate 9-phosphate synthase = [N-acetylneuraminate 9-phosphate synthase subunit]2
The native apparent molecular mass was determined by gel filtration chromatography [Chen02].
This enzyme catalyzes a critical reaction in sialic acid biosynthesis, the condensation of phosphoenolpyruvate with N-acetyl-D-mannosamine 6-phosphate. Unlike the bacterial enzyme that uses N-acetyl-β-D-mannosamine as substrate, the animal enzyme uses the 6-phosphorylated derivative to produce N-acetyl-β-neuraminate 9-phosphate (see pathways CMP-N-acetylneuraminate biosynthesis I (eukaryotes) and CMP-N-acetylneuraminate biosynthesis II (bacteria)).
A key difference also exists in the human sialic acid synthase versus rat (this enzyme) and mouse N-acetylneuraminate 9-phosphate synthase enzymes. The human enzyme can also utilize α-D-mannose 6-phosphate to produce 2-keto-3-deoxy-D-glycero-D-galacto-nononate 9-phosphate in this reaction (see pathway CMP-2-keto-3-deoxy-D-glycero-D-galacto-nononate biosynthesis), whereas the rodent enzymes cannot (reviewed in [Tanner05]). Mutagenesis studies of the recombinant human enzyme revealed that a single mutation resulting in substitution of Thr for Met at position 42 eliminated the 2-keto-3-deoxy-D-glycero-D-galacto-nononate 9-phosphate synthase activity without affecting N-acetyl-β-neuraminate 9-phosphate synthase activity [Hao06].
The native rat liver enzyme was purified to homogeneity and was determined to be a homodimer [Chen02]. Although the human sialic acid synthase [Lawrence00] and mouse N-acetylneuraminate 9-phosphate synthase [Nakata00] enzymes have been cloned, the rat enzyme has not.
The apparent molecular mass of the subunit was determined by SDS-PAGE [Chen02].
Molecular Weight of Polypeptide: 37.0 kD (experimental) [Chen02 ]
Molecular Weight of Multimer: 75.0 kD (experimental) [Chen02]
Enzymatic reaction of: N-acetylneuraminate 9-phosphate synthase
Synonyms: N-acetylneuraminate phosphate synthase, N-acetylneuraminic acid phosphate synthase, N-acetylneuraminic acid 9-phosphate synthase, sialic acid (N-acetylneuraminic acid) synthase, sialic acid synthase
EC Number: 18.104.22.168
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.
The reaction is favored in the direction shown.
The enzyme was highly specific for N-acetyl-D-mannosamine 6-phosphate and did not utilize D-glucosamine 6-phosphate, β-D-fructofuranose 6-phosphate, N-acetyl-α-D-glucosamine 1-phosphate, N-acetyl-D-glucosamine 6-phosphate, or N-acetyl-β-D-mannosamine as substrate. pyruvate could not replace phosphoenolpyruvate [Chen02].
The rat enzyme also did not use α-D-mannose 6-phosphate as substrate and therefore lacked 2-keto-3-deoxy-D-glycero-D-galacto-nononate 9-phosphate synthase activity [Chen02].
The mechanism of this condensation reaction remains to be completely elucidated, although possible mechanisms have been considered that involve either C-O, or P-O bond cleavage (reviewed in [Tanner05]).
Chen02: Chen H, Blume A, Zimmermann-Kordmann M, Reutter W, Hinderlich S (2002). "Purification and characterization of N-acetylneuraminic acid-9-phosphate synthase from rat liver." Glycobiology 12(2);65-71. PMID: 11886839
Hao06: Hao J, Vann WF, Hinderlich S, Sundaramoorthy M (2006). "Elimination of 2-keto-3-deoxy-D-glycero-D-galacto-nonulosonic acid 9-phosphate synthase activity from human N-acetylneuraminic acid 9-phosphate synthase by a single mutation." Biochem J 397(1);195-201. PMID: 16503877
Lawrence00: Lawrence SM, Huddleston KA, Pitts LR, Nguyen N, Lee YC, Vann WF, Coleman TA, Betenbaugh MJ (2000). "Cloning and expression of the human N-acetylneuraminic acid phosphate synthase gene with 2-keto-3-deoxy-D-glycero- D-galacto-nononic acid biosynthetic ability." J Biol Chem 275(23);17869-77. PMID: 10749855
Nakata00: Nakata D, Close BE, Colley KJ, Matsuda T, Kitajima K (2000). "Molecular cloning and expression of the mouse N-acetylneuraminic acid 9-phosphate synthase which does not have deaminoneuraminic acid (KDN) 9-phosphate synthase activity." Biochem Biophys Res Commun 273(2);642-8. PMID: 10873658
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