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The amino acid substitutions resulting from single-base substitution in the natural genetic code have been compared with those resulting from single-base substitutions in computer-generated random codes. Considering the amino acid properties of molecular weight, polar requirement, number of dissociating groups, pK(1)', isoelectric point, and alpha-helix forming ability, it is concluded that, for the natural code, single-base substitution in the first position of the codon tends to result in the substitution of an amino acid more similar to the original amino acid than would be expected from a random code. In the natural code, the second position of the codon plays the largest role in determining the properties of the amino acid.
C. Alff-Steinberger (Wed,) studied this question.