Protein folding and the genetic code: An alternative quantitative model

A linear equation is presented which quantitatively accounts for the tendency of amino acids to be found at the surface of globular proteins as a function of side-chain structure. The parameters are a steric effect constant, and indicator variables one of which represents the presence or absence of an OH or NH group, the other that of a strongly basic group. The distribution of amino acids between surface and interior of globular proteins is related to the second letter of the genetic code.