|  |  |  |  |  |  |  |  |  |  |  | 
   
    | • | Many proteins
    exist in an anaerobic environment 
 |  | 
   
    |  | 
   
    |  | – | Lose cofactors
    such as iron-sulfur clusters in oxygen 
 | 
   
    |  | environment 
 |  | 
   
    |  | 
   
    |  | – | Need to reproduce
    redox state of cofactors such as 
 |  | 
   
    |  | FAD+
    and NAD+ 
 |  | 
   
    |  | 
   
    | • | Many
    crystallographers need to see different redox 
 |  | 
   
    |  | states of protein
    conformations for biological studies 
 |  |