Table 3. Mutational effects on the catalytic activity (k _cat/K _m ratio) and thermal stability (ΔT _m) of Sfβgly proteins.

Mutation position	kcat/K m ratio (mutant/wt)			ΔTm (K)
	NPβglc	NPβgal	NPβfuc
49	0.5	0.06	0.7	−7.2
54	0.02	0.005	0.02	−0.2
57	0.77	0.12	0.8	−1.0
62	0.09	0.03	0.18	−5.5
98	-	-	-	−2.1
112	1.5	0.19	0.38	−0.3
143	0.0004	0.0003	0.0005	−7.2
188	0.0002	0.0011	0.0012	3.2
195	0.11	0.01	0.03	0.1
196	0.06	0.01	0.06	0.0
203	0.06	0.04	0.21	0.8
223	0.30	0.05	0.075	6.0
278	0.005	0.02	0.02	5.8
309	0.15	0.02	0.02	−7.1
398	-	-	-	nd
445	1.1	1.5	0.27	−1.9
452	-	-	-	−2.8
460	0.0012	0.0037	0.0044	−12.2

Only mutational effects higher than a 4-fold change in the k _cat/K _m ratio (0.25>k _cat/K _m ratio >4) were considered significant for the enzymatic activity. Mutational effects on the thermal stability were considered relevant only for ΔT_m>2.5 K. –, no activity; nd, not determined; wt, wild-type.