UDPGlcNAc Epimerase

Figure 5.66 Mechanism of action of (a) UDPGlcNAc epimerase and (b) hydrolysing UDPGlcNAc epimerase.

The structure revealed the basis for the pronounced allosteric nature of the enzyme. Initial rates of UDPGlcNAc isomerisation give a Hill coefficient [eqn. (5.20), Figure 5.5] of 2.29 and epimerisation of UDPManNAc does not take place except in the presence of its epimer. The asymmetric unit of the crystals of UDPGlcNAc 2-epimerase contains four copies of the enzyme arranged as two similar copies of the biological homodimer, with each dimer composed of one... 

Other epimerases using this mechanism appear to be UDPGlcNAc 4-epimerase (indeed, the UDPGal 4-epimerase from some species has a small amount of this activity), UDPXyl 4-epimerase and UDPGlcA 4-epimerase. The mechanism is not confined to transiently oxidising position 4 an enzyme... 

Fig. 8. (B) Possible pathway for the action of UDPGlcNAc 2-epimerase (from Biochemistry 9, 885, 1970).

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