TABLE 2.

Comparison of conserved transketolase residues with those in DXPase-A and DXPase-B^a

DXPase-A residue	DXPase-B residue	Transketolase residue	Function	Reference(s)
H80	H79	H69	Stabilization of reaction intermediate; binds C-1 hydroxyl of donor substrate	53
H49	H48	H30	Acid-base catalyst (proton acceptor or donor)	53
H258	H257	H263	Acid-base catalyst (proton acceptor or donor)	53
D152	D151	D157	Metal binding (side chain)	42
N181	N180	N187	Metal binding (side chain)	42
M183	M182	I189	Metal binding (main-chain oxygen)	42
D429	D428	D477	Binds C-2 hydroxyl of acceptor substrate; enantioselectivity of enzyme	30, 42
H433	H432	H481	Transition-state stabilization	53
E372	E372	E418	Binds N-1′ nitrogen of TPP cofactor (essential for catalytic activity)	42, 52
R480	R479	R528	Phosphate binding of substrate	31, 42
Y394	Y393	F442	Interaction with pyrimidine ring of TPP	42
F397	F396	F445	Interaction with pyrimidine ring of TPP	42
Y402	Y401	Y448	Interaction with pyrimidine ring of TPP	42

^aImportant conserved residues from S. cerevisiae transketolase and the similarly conserved residues in R. capsulatus DXPase-A and DXPase-B are compared. The proposed function of these residues is based on numerous studies of transketolases reported in the literature.