In the case of the OHR experiment, the enzyme was first reduced under anaerobic conditions with a sub-equivalent amount of progesterone (1:0.8), thus avoiding the excess progesterone that would interfere with the enzyme reoxidation. In each measurement, one glass syringe was filled with the buffer solution of the reduced AcmB, and the second syringe was filled with the buffer solution of 2,6-dichloroindophenol (DCPIP) and 2-methoxyethanol (EGME). The solutions were treated with argon for several minutes before the experiment. The OHR reaction was followed at 616 nm and 20 o C in 50 M DCPIP in 8% EGME with 10 M AcmB in the buffer solution. The obtained traces were fitted with double exponential functions yielding eigenvalues λobs.