Unusual 1H NMR chemical shifts support (His) Cepsilon 1---H{middle dot}{middle dot}{middle dot}O==C H-bond: Proposal for reaction-driven ring flip mechanism in serine protease catalysis -- Data Supplement - Supplemental Data -- Proceedings of the National Academy of Sciences

Supplementary material for Ash et al. (2000) Proc. Natl. Acad. Sci. USA 97 (19), 10371-10376.

Table 4.
Derivation of protein chemical shift models

	Model
	Ösapay & Case (6)	Herranz et al.(7)	Williamson & Asakura(8)
No. of proteins, CH fit	17	3	8
No. of C-H protons fit	5,678	265	768
No. of a protons fit	1,553	265	768
Glycine protons	Excluded	Include better of 2	If 2, average; else discard
b Protons	Averaged	None	None
Other protons	All but pH depend	None	None
Ring-current model	Haigh & Mallion (13)	Johnson & Bovey (14)	Johson & Bovey (14)
Ring intensity factors	5 (empirical)	2 (literature values)	5 (empirical)
Electric field term	Yes*	No	Yes*
R value for C-H	0.88	0.79	Typ. 0.85
SE	± 0.23	± 0.29	Typ. ± 0.27
No. of proteins, NH fit	17	3	15^†
No. of N-H protons fit	1,627	239	1,509^†
Ring-current model	Haigh & Mallion (13)	Johnson & Bovey (14)	Haigh & Mallion (13)
Electric field term	Yes	No	No
R value for N-H	0.58	0.76^‡	0.67^§
SE	± 0.62	± 0.45^‡	± 0.54^§

*Electric field term makes a modest, but systematic improvement in fit.

^†Asakura et al. (9). ^‡Slightly different coefficients for N- H, A_OCN = 30.5, C_CO = -9.54, using our convention. ^§Slightly different coefficients for N- H, A_CO = -11, B_CO = -5, A_CN = -7, and B_CN =1, using our convention.