This predicted behavior indeed fits the respective experimental conditions since all EPR experiments with BSS or other FAE to date were conducted in cell extracts , which always contain enough product and leftover substrates to saturate the enzymes (e.g. from the growth of the cells on toluene). This suggests that the observed change of the glycyl radical signal in EPR spectra upon incubation in D2O is facilitated by the binding of either the substrates of the product. This would allow BSS to attain a conformation that exhibits lower H transfer barriers from Cys493 to the glycyl radical and speeds up the H/D exchange process.