The distribution of isoelectric points of human soluble proteins and in particular of the enzyme products of 88 human gene loci

The isoelectric points of the 'primary' isozymes coded for by 88 human gene loci have been determined. The distribution was found to be bimodal with an antimode at the 'physiological pH'. Soluble human proteins have the same distribution and this appears to be characteristic of soluble mammalian proteins in general. There may be some correlation with function, mitochondrial enzymes being more basic and hydrolytic enzymes being more acidic than other classes of enzymes. The bimodal distribution can be explained in terms of the buffering effects of the charged amino acids. Most proteins would thus appear to be charged at neutral pH values.