Table 1. ^2hJ_NN Values, Amide Donor ¹H Chemical Shifts, and Histidine ¹⁵Nδ1 and ¹⁵Nε2 Chemical Shifts Observed for N–H···Nδ1 Helix-Capping H-Bonds^a.

labelb	protein	distalc	|2hJNN| (Hz)	1H (ppm)	δ15Nε2 (ppm)	δ15Nδ1 (ppm)
	CtrHb, Md,e	CN	5.3 ± 0.2	11.41	ndf	254.9
A	CtrHb, md	CN	5.2 ± 0.2	11.39	166.6	254.9
B	CtrHb, M	CN	5.0 ± 0.1	11.17	166.5	255.1
C	CtrHb-B	CN	4.0 ± 0.3	10.45	168.6	249.6
D	THB1, Mg	CN	4.8 ± 0.1	11.18	166.4	256.6
E	THB1, mg	CN	4.6 ± 0.3	11.28	166.9	256.9
F	Syn7002h GlbN	His	4.7 ± 0.2	10.77	166.9	256.4
G	Syn7002 GlbN-A	His	4.8 ± 0.2	10.97	167.3	256.6
H	Syn6803i GlbNg	CN	5.0 ± 0.2	11.34	165.9	257.7
I	Syn6803 GlbN-Ag	CN	4.8 ± 0.2	11.40	166.1	258.0
J	Syn6803 GlbN	His	4.9 ± 0.2	11.14	165.8	257.4
K	Syn6803 GlbN-A	His	4.9 ± 0.2	11.28	166.0	257.5
L	Syn6803 GlbN-B	His	4.5 ± 0.2	10.93	166.9	255.3
M	Syn6803 GlbN-AB	His	4.3 ± 0.2	10.87	167.6	254.5
N	Syn6803 GlbN-B	CN	5.4 ± 0.1	11.40	166.0	256.9
O	Syn6803 GlbN-AB	CN	5.0 ± 0.1	11.29	166.4	257.1
P	ferric cyt b5	His	5.0 ± 0.1	10.88	165.0	250.5
Q	ferrous cyt b5	His	5.0 ± 0.1	10.94	165.3	250.6
R	apocyt b5j	−	5.3 ± 0.1	11.15	165.0	250.3

^aMeasured at 313 K, 10% D₂O, and pH 7.0–7.2 on proteins containing ferric heme iron unless otherwise noted.

^bAs annotated in Figure 5.

^cDistal ligand to the heme iron.

^dM, major heme isomer; m, minor heme isomer.

^eMeasured at 283 K.

^fNot determined.

^gMeasured at pH 7.3–7.5.

^hSyn7002, Synechococcus sp. PCC 7002.

ⁱSyn6803, Synechocystis sp. PCC 6803.

^jMeasured at 298 K.