Table 1.

Kinetic parameters of maize EPSPS with mutations found in glyphosate-resistant weeds

Values represent mean ± S.E. for at least 4 sets of rate measurements. For assay procedure and analysis, see “Experimental procedures.” Values for K_m were obtained by varying one substrate, with the other present at saturation (10 times its K_m) and therefore are apparent K_m. Values shown for k_cat are those obtained from substrate saturation with PEP, which in no case differed significantly from those obtained with S3P.

	kcat	Km PEP	kcat/Km	Ki	Km S3P	kglya	(kcat/Km) × Kib
	min−1	μm		μm		min−1
Zm nativec	1630 ± 14	9.5 ± 0.3	172	0.066 ± 0.003	13.2 ± 0.6	<lodd	11
Zm-P106Se	1540 ± 12	11.5 ± 0.5	134	0.33 ± 0.02	15.4 ± 0.4	2.3 ± 0.07	44
Zm-P106Lf	1760 ± 10	47.0 ± 1.1	37.5	3.94 ± 0.17	27.6 ± 0.7	5.7 ± 0.17	148
Zm-P106L+3g7	1450 ± 22	10.3 ± 0.7	140	2.34 ± 0.18	17.5 ± 0.6	10.1 ± 0.1	329
Zm-TIPS+2h	105 ± 1.0	16.2 ± 0.7	6.5	731 ± 36	27.5 ± 0.7	25.5 ± 0.4	4740
Zm-T102Si	1600 ± 13	30.9 ± 1.0	51.8	0.69 ± 0.02	28.8 ± 0.6	2.0 ± 0.09	35.7
Ha-T102Sj	1800 ± 13	30.4 ± 0.8	59.1	0.75 ± 0.03	21.5 ± 0.5	2.4 ± 0.08	44.3

^a Enzyme turnover (min⁻¹) at 30 μm PEP and S3P, 1 mm glyphosate (see “Results” for rational as a fitness parameter).

^b Calculated with K_m for PEP.

^c Native Z. mays EPSPS having the amino acid sequence described in the legend to Fig. 2.

^d lod; limit of detection calculated as Blank + 3xSD of blank. The value is 1.5 min⁻¹.

^e A mutation found in multiple species of glyphosate-resistant weeds, here created in maize EPSPS.

^f A mutation found in several species of glyphosate-resistant weeds, here created in maize EPSPS.

^g Variant captured from the initial combinatorial library (see “Results”), having P106L and three additional mutations (A100S, E301S, A337S).

^h Variant captured from the initial combinatorial library, having T102I, P106S and two other mutations (T277G, A337S).

ⁱ A mutation found in a glyphosate-resistant population of T. procumbens, here created in maize EPSPS.

^j A mutation found in a glyphosate-resistant population of T. procumbens, here created in H. annuus (sunflower) EPSPS.