TABLE 1.

Kinetic parameters of wild-type and mutant GST-β4GalT7

Kinetic parameters towards donor (UDP-Gal) and acceptor (4-MUX) substrates were determined as described under “Experimental Procedures.” The results are the mean values of three independent determinations ± S.D. on assays performed in duplicate.

Enzyme	kcat	UDP-Gal		4-MUX
		Km	kcat/Km	Km	kcat/Km
	min−1	mm	min−1·mm−1	mm	min−1·mm−1
GST-β4GalT7	90.5 ± 2.3	0.22 ± 0.02	425	0.35 ± 0.02	250
Y194A	NDa	ND		ND
Y194F	ND	ND		ND
H195A	115.9 ± 9.7b	0.40 ± 0.02b	291	0.64 ± 0.02b	180
H195Q	97.4 ± 2.4b	0.33 ± 0.02b	295	0.55 ± 0.02b	177
H195R	89.6 ± 1.3	0.32 ± 0.02b	295	0.35 ± 0.03	242
Y196A	ND	ND		ND
Y196F	30 ± 1.1b	0.34 ± 0.06b	88	1.06 ± 0.06b	28
Y199A	ND	ND		ND
Y199F	72.3 ± 5.8b	0.32 ± 0.02b	243	0.59 ± 0.06b	113
R226A	53.6 ± 2.0b	0.34 ± 0.03b	171	0.44 ± 0.05b	112
R226K	81.1 ± 2.9b	0.29 ± 0.02b	282	0.46 ± 0.01b	175
R270A	46.4 ± 0.2b	0.27 ± 0.01b	184	0.60 ± 0.02b	72
R270K	48.7 ± 1.5b	0.37 ± 0.02b	139	0.54 ± 0.07b	85

^a ND indicates that no kinetic constant could be determined using excess acceptor or donor substrate.

^b The results were analyzed with Student's t test and considered as significant when p < 0.05.