Table 2.

Observed catalytic activities for designed proteins

Site	Fenton*		SOD	Udenfriend†
	kcat, s−1	Km, mM	k, 106 M−1⋅s−1	k, s−1
G1	0.80	1.70	0.75	9.70
G2	0.70	1.60	0.10	0.01
G3	0.50	0.60	0.10	16.00
S1‡	1.50	6.50	2.30	0.01
S2	0.50	1.30	6.40	0.01
D1	0.03	0.14	3.30	30.00

Two types of background rates were determined: the free metal salt in buffer and precursor protein metal complexes. Background activity upper limits: SOD, k ∼ 1⋅10⁶ M⁻¹⋅s⁻¹; Udenfriend, k ∼ 0.050 s⁻¹; Fenton, k_cat ∼ 0.005 s⁻¹, K_m(H₂O₂) ∼ 20 mM. 

^*Absence of ascorbate reduces rates 100- to 1,000-fold, indicating that intrinsic H₂O₂ disproportionation is not a major contributing factor. 

^† Pseudo first-order rate constant: M catechol, M⁻¹; 1:1 Fe/protein, s⁻¹. 

^‡ Although results for S1 are reported, this design is omitted from the analysis of trends (see text), because its weak metal affinity precludes formation of a 1:1 complex in the absence of substantial concentrations of free metal.