Michaelis-Menten analysis was performed on these enzyme/substrate pairs. Table lists the Km, Vmax and kcat/Km of each. Overall, catalytic efficiency for Te reduction is notably less than for Se reduction, indicating that the SeR is specialized for Se reduction. Among the Te species, catalytic efficiency for TeO32-improves by a factor of ~4, whereas catalytic efficiency for GS-Te-SG is unchanged within experimental error. Overall, the evolution of catalytic efficiency from favoring oxidized glutathione substrates to increasingly favor chalcogenide oxyanion substrates is consistent for both Se and Te based substrates.