Plots of initial enzyme velocity vs. concentration for both GRLMR and SeR with all 3 substrates are shown in Figure . The data was fitted with the Michaelis-Menten enzyme kinetic model in Origin . Table gives the Km, Vmax and kcat/Km values derived from for each enzyme/substrate pair. Because the evolved enzyme has a dramatically increased catalytic efficiency toward Selenite and Selenate, coupled with substantially decreased activities toward GSSG and GS-Se-SG, we name the evolved enzyme Selenium Reductase (SeR). GRLMR and SeR, like glutathione reductase (GSHR), do not conform perfectly to Michaelis-Menten enzyme kinetics. The main deviation from classic Michaelis-Menten kinetics is substrate inhibition of the enzyme at higher substrate concentrations. This leads to some uncertainty in Vmax determination. In some cases (noted with † in table ), the algorithmic fits to Michaelis-Menten models were clearly flawed due to substrate inhibition resulting in artifactually low Vmax values. These nonlinear regression fits are shown in figures S1 and S2, accompanied by explanation for which Vmax values were estimated.