Table 5.

Relative kinetic parameters of retro-aldol cleavage reactions catalysed by eTA mutant forms with the threo and erythro isomers of l-threonine.

Substrate	H83F/H126F				F87A				F87D				K222A
	kcata	Km	$\frac{k_{\mathit{\text{cat}}}}{K_m}$	S.Pb	kcat	Km	$\frac{k_{\mathit{\text{cat}}}}{K_m}$	S.P.	kcat	Km	$\frac{k_{\mathit{\text{cat}}}}{K_m}$	S.P.	kcat	Km	$\frac{k_{\mathit{\text{cat}}}}{K_m}$	S.P.
L-allo-Threonine	0.008	31	0.0003	11.5	0.7	1.3	0.6	105	0.5	1.7	0.3	361	0.4	5.0	0.07	112
L-Threonine	0.004	1.1	0.003		0.4	0.4	0.8		0.2	1.3	0.1		0.4	3.7	0.1

^aValues in the table are the ratio between the parameters determined with wild type and mutant enzymes, and shown in Table 4 (e.g. k_cat mutant enzyme/k_cat wild type enzyme). In the table, ratios higher than 2 are in bold, while ratios lower than 0.5 are underlined.

^bSubstrate Preference, expressed as the ratio between the specificity constant (k_cat/K_m) determined with the erythro substrate and the specificity constant determined with the threo substrate. S.P. of the wild type enzyme is 153