Size distrbution of polypeptide chains in cells

THE monomer molecular weight distribution in the total proteins of various cell types is unknown. A list has been compiled1 for purified proteins of which the molecular weights of the monomeric subunits are known. Large polypeptides are rare; only about 20 per cent of the listed monomeric proteins are larger than 80,000 daltons. The overall size distribution of cellular proteins may be inferred from such data, but it would never be possible to be sure that these extensively purified proteins represented a truly random sample.