Chelators per protein molecule

A simple calculation is instructive. Consider reaction with one type of side chain of which there are, say, dozens on each protein molecule (in identical environments) and suppose we wish to have an average of one chelator per protein molecule. Poisson statistics are appropriate to describe a situation like this (23), where the number of labeled side chains will be a small fraction of the number of available side chains. 

However, if a reagent would react only with a single site on a macromolecule, then a chemically homogeneous product having one chelator per protein molecule could be formed. Alkylation of the single sulfhydryl group of albumin with a haloacetyl reagent probably comes reasonably close to this situation. 

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