Epimerases acetyl glucosamine epimerase

The amino acid sequence deduced from ORF 23 (mnaA) shared homology with bacterial A-acetylglucosamine 2-epimerases that convert A-acetyl-glucosamine into A-acetylmannosamine, a precursor of sialic acids. ORF 9 and ORF 24 (neuB) both produce polypeptides that exhibited 25 and 31%... 

Lucka, L. Krause, M. Danker, K. Reutter, W. Horstkorte, R. Primary structure and expression analysis of human UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase, the bifimctional enzyme in neuraminic acid biosynthesis. FEBS Lett., 454, 341-344 (1999)... 

Stasche R, Hinderlich S, Weise C et al. (1997) A bifunctional enzyme catalyzes the first two steps in N-acetylneuraminic acid biosynthesis of rat liver. Molecular cloning and functional expression of UDP-N-acetyl-glucosamine 2-epimerase/N-acetylmanno-samine kinase. J Biol Chem 272, 24319-24324. 

The biosynthetic pathway for sialic acid formation in liver was well established nearly thirty years ago, by the elegant work from the groups of Roseman [9-11] and Warren [12] (Figure 1). The enzymatic conversion of UDP-A-acetyl glucosamine to A-acetylmannosamine is the critical step in the overall synthesis of sialic acid because the activity of this epimerase is controlled downstream in the pathway by feedback inhibition by CMP-A -acetylneuraminic acid [13]. Thus, production of ManNAc as a precursor for sialic acid biosynthesis is a closely regulated cellular process. 

An elegant continuous process for N-acetylneuraminic acid synthesis was developed by introducing the N-acetylneuraminic acid-2-epimerase for epimerization of N-acetyl glucosamine 119 and integrating the epimerization with synthesis in an enzyme-membrane reactor [151]. Although this process has an excellent space-time yield, the epimerase enz)une is not freely available and the product stream is very dilute and chromatography is required for purification, making scale-up difficult. 

Tabata, K., Koizumi, S., Endo, T. and Ozaki, A., Production of A-acetyl-D-neuraminic acid by coupling bacteria expressing N-acetyl-o-glucosamine 2-epimerase and N-acetyl-o-neuraminic acid synthetase. Enzyme Microb. Technol. 2002, 30, 327-333. 

We propose that the first step in NDP-kasugamine biosynthesis is 2-epimeriza-tion of the postulated UDP-A -acetyl-D-glucosamine precursor, which is suggested by the similarity of the KasQ protein with known UDP-(Af-acetyl-)D-glucosamine 2-epimerases and catalyzes the conversion to UDP-N-acetyl-D-mannosamine. To... 

N-Acetylglucosamine 2-epimerase, N-ACYLGLUCOSAMINE 3-EPIMERASE N-ACETYLGLUCOSAMINE KINASE N-Acetyl-D-glucosamine 1-phosphate, PHOSPHOACETYLGLUCOSAMINE MUTASE... 

We describe here the enzymological characteristics and application of isomerases, especially D-xylose (glucose) isomerase, phosphoglucose isomerase, triose phosphate isomerase, L-rhamnose isomerase, L-fucose isomerase, maleate cis-trans isomerase, and unsaturated fatty acid cis-trans isomerase. N-Acetyl-D-glucosamine 2-epimerase is not an isomerase, but for convenience we will also describe the characteristics and use of the enzyme because this section deals with sugar-metabolizing enzymes. 

Figure 17-33. Synthesis of N-acetylneuraminate (Neu5Ac) from N-acetyl-D-glucosamine (GIcNAc) and pyruvate through N-acetyl-D-mannosamine (ManNAc) with N-acetylneuraminate and N-acetyl-D-glucosamine 2-epimerase. Reprinted from Maru et al.I259].

By application of N-acylglucosamine 2-epimerase it is possible to start with the inexpensive N-acetyl-D-glucosamine instead of N-acetyl-D-mannosamine (Fig. 19-42). The epimerase is used for the in situ synthesis of N-acetyl-D-mannosamine... 

I. Maru, J. Ohnishi, Y. Ohta, Y. Tsukada, Simple and large-scale production of N-acetylneuraminic add from N-acetyl-D-glucosamine and pyruvate using N-acyl-D-glucosamine 2-epimerase and N-acetyl-neuraminate lyase, Curb. Res. 1998, 306, 575-578. 

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