Hi, Is there a straight-forward way to estimate the amount of missing electron > density that a particular protein structure is missing based on the > difference between Fo and Fc? >
Any refinement or map calculation software that uses likelihood-based approach does this routinely. In phenix.refine and phenix.maps I coded this approach : Acta Cryst. (2002). A58, 270-282. Here it calculates alpha/beta parameters by comparing Fo and Fc taken from free set. alpha is a function of model error, and beta is proportional to amount of missing scattering. If you look up the formulas it should be possible to convert alpha into error in coordinates (in A) and beta into number of missing atoms (of some general type). ML based estimate of error in model that phenix.refine reports is actually done this way. Pavel
