terminal 
 oxidases catalyze four - electron reduction of oxygen to 
 water , and the energy harvested is utilized to drive the synthesis 
 of adenosine triphosphate . while much effort has been made to design 
 a catalyst mimicking the function of terminal oxidases , most biomimetic 
 catalysts have much lower activity than native oxidases . herein we 
 report a designed oxidase in myoglobin with an o2 reduction 
 rate ( 52 s1 ) comparable to that of a native cytochrome 
 ( cyt ) cbb3 oxidase ( 50 s1 ) under identical conditions . 
 we achieved this goal by engineering 
 more favorable electrostatic interactions between a functional oxidase 
 model designed in sperm whale myoglobin and its native redox partner , 
 cyt b5 , resulting in a 400-fold electron 
 transfer ( et ) rate enhancement . 
 achieving high activity equivalent 
 to that of native enzymes in a designed metalloenzyme offers deeper 
 insight into the roles of tunable processes such as et in oxidase 
 activity and enzymatic function and may extend into applications such 
 as more efficient oxygen reduction reaction catalysts for biofuel 
 cells .