Table 2. Active site residue identities and geometric values.

Stereospecificity	Inverting			Retaining
Example enzyme	GlcAT-I	GalT1	GnT1	LgtC	GTA	Extl2	ManT
PDB(1)	1V84	1TVY	2AM3	1GA8	2RJ7	1OMZ	2WVL
PDB(2)	1KWS	1TW5
Nu – C1 dist.	4.4 Å	4.2 Å	4.0 Åa	2.2 Å	2.5 Å
<Nu-C1-O3	160°	165°	151°a	90°	74°	NA	NA
Nu – O3 dist.	5.8 Å	5.6 Å	5.4 Åa	2.8 Å	2.2 Å
O3– nearest polar X	H2Ob	K279	Y184	H78	K346	H2Ob	Y268
O3- X dist.	4.4 Å	4.4 Å	5.4 Å	4.7 Å	5.6 Å	3.8 Å	4.4 Å
<X-O3-C1	91°	80°	87°	171°	149°	131°	59°
C1 nearest polar Y	H308	W314	D211	Q189	E303	R293	D167
C1-Y dist	3.6 Å	4.5 Å	5.2 Å	3.5 Å	4.8 Å	3.7 Å	3.5Å
<Y-C1-O3	67°	75°	71°	162°	155°	167°	142°
O5 nearest polar Z	R156	W314	D291	Q189	R352	R293	D168
O5-Z dist.	5.9 Å	3.4 Å	3.9 Å	4.2 Å	5.8 Å	3.2 Å	3.8 Å
<Z-O5-C1	113°	123°	96°	82°	83°	97°	68°
c c	H2Ob	H2Ob	H2Ob	D103	D211	H2Ob	NA
<bMc c	89°	82°	87°	105°	116°	101°	NA
f c	D196	H347	H2Ob	D105	D213	H2Ob	N313
<bMf c	114°	104°	95°	92°	90°	88°	82°

With the exception of the GTA neutron diffraction studies [44] hydrogen atoms are not directly observed, so distances are given between centers of non-hydrogen atoms. Italic enzyme names indicate the model did not contain an acceptor molecule.

^aPDB 2AM3 has a glycerol molecule modeled as an acceptor.

^bIt is likely that the active species are not actually water molecules, but residues in disordered regions of the polypeptide.

^c b, c and f are octahedral binding partners to the coordinated metal atom M as described in Figure 2 .