Nitrogenase rate limiting step

The rate-limiting step of nitrogenase is the dissociation of the reduced MoFe protein from the oxidized Fe protein and has a rate constant k = 6.4 0.8 sec-1. An implicit assumption in the multistep mechanism shown in Figure 13 is that the three elementary reactions coupling each state of the MoFe protein are unperturbed by the reduction level of the large protein. This assumption has been verified for the species E0 and ) [73],... 

In Figure 13 the symbol, E represent various states of the enzyme, with the subscript n corresponding to the total number of electrons transferred to the MoFe-protein. The arrows which interconnect E and E +j actually comprise three elementary reactions shown at the foot of the Figure (i) the binding of the reduced Fe-protein to the oxidised MoFe-protein to form an adduct (ii) transfer of an electron from Fe-protein to MoFe-protein within the adduct and (iii) dissociation of the adduct. This same sequence of elementary reactions is performed at each step around the cycle with (it is assumed) unchanged rate constants. The rate-limiting step of nitrogenase is the dissociation of the component proteins (k = 6.4 s- ). 

Cornish-Bowden, 1977) which is much faster than the enzyme turnover time. Therefore, a possible rate-limiting step in nitrogenase turnover is the release of MgADP from the oxidized Fe protein when it is bound to the MoFe protein. 

---