. Author manuscript; available in PMC: 2014 Mar 6.

Published in final edited form as: J Am Chem Soc. 2013 Feb 19;135(9):3485–3493. doi: 10.1021/ja310180c

Table 2.

Bond order and bond length at the transition-state of the NMN pyrophosphorolysis catalyzed by HsNAMPT and comparison with other reactions catalyzed by NAD-utilizing enzymes

system	r_C-LG(r_C-N)		r_C-Nu(r_C-X)^a
	bond order^b	Å	bond order	Å
DT NAD hydrolysis (O)^a	0.02	2.65	0.03	2.46
NAMPT NMN PPi (O)	0.06	2.35	0.02	2.60
PT NAD hydrolysis (O)	0.11	2.14	0.001	3.50
PT NAD G_iα1 (S)	0.13	2.10	0.09	2.55
PT NAD α_i3C20 (S)	0.15	2.06	0.12	2.47
DT NAD eEF-2 (N)	0.18	1.99	0.03	2.58

The nature of the atom nucleophile depends on the system studied. It is an oxygen atom (O) for the NAD hydrolysis catalyzed by both Diphtheria and Pertussis toxins (DT and PT, respectively) or for the pyrophosphorolysis of NMN catalyzed by NAMPT. It is a sulfur atom (S) for the ADP-ribosylation of G_iα1 and _αi3C20 peptides by PT toxin. Finally, it is a nitrogen atom (N) when the DT toxin ADP-ribosylates eukaryotic elongation factor 2 (eEF-2).

Pauling bond orders are calculated using the relation ni = e⁽^r^-^r^i)/0.3, where r is the bond length of a single bond (i.e. r_C-N = 1.48 Å, r_C-S = 1.83 Å, r_C-O = 1.44 Å) and r_i is the interatomic distance between C1′ and the atom of interest (i.e. r_C-LG and r_C-Nu).