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Feasibility of MAD experiment |
On the CCP4 Bulletin Board the following was presented:
Copper is a competitive inhibitor of my enzyme. I have crystals which have turned blue on soaking with copper salt. Assuming the worst scenario where there is only one copper bound to one enzyme (350 amino acids) would it be worth it to do a MAD experiment ? Thanks
There a some rules of thumb to check whether a MAD experiment is feasible or not :
Dano ~ 1/sqrt(2) sqrt(Na/Np) 2f"/<fp> Diso ~ 1/sqrt(2) sqrt(Na/Np) Df'/<fp>where
Na | number of anomalous scatterers (1 in your worst case) |
Np | number of protein atoms (approx 350x11= 3850) |
f" | f" of your anomalous scatterer (best is 4 electrons with Cu) |
Df' | difference in f' between 2 lambda (max 8 electrons with Cu) |
<fp> | average scattering factor of your protein atoms (6.7) |
However, these are not hard rules....