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. 2009 Dec 10;38(5):1738–1748. doi: 10.1093/nar/gkp1093

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© The Author(s) 2009. Published by Oxford University Press.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 6. — The role of a conserved aspartic acid. (A) In TK, the Asp96 residue plays a noncatalytic role. (B) In NrK, the Asp36 plays a dual role in stabilizing the bound Mg²⁺ and activating the nicotinamide riboside oxygen. (C) By contrast, in HlAIPT, the Asp62 plays an essential role as a general base. (D) The proposed catalytic mechanism of HlAIPT involves Asp62, but also Ser44 for binding to DMAPP via Mg²⁺ ion and Thr39 and Arg184 for stabilizing the negative charge developed in the leaving pyrophosphate group.