A statistical examination of self-ordering of amino acids in proteins

Steinman and Cole (1967) have claimed that amino acids will naturally assume a nonrandom sequence when polymerized into polypeptides. They based their claim on a comparison of the frequency with which various dipeptide bonds formed in a dilute solution of amino acids to the various depeptide frequencies actually observed in ten proteins. Although the trends in the normalized frequencies go in the same direction, a statistical examination of the two sets of frequencies indicates that there is no correlation at all between experimental dipeptide frequencies and actual depeptide frequencies based on the chi-square tests.