| aa | : | single letter amino acid abbreviations |
Returns: 0..21
Synopsis: This function converts a one letter abbreviation for an amino acid to an posint between 1..20 according to the standard ordering of amino acids (see beginning of this section). If aa is not a amino acid abbreviation, the value 0 is returned. If aa is the unknown amino acid X, then the value 21 is returned. Examples:
> AToInt('V');
> AToInt('X');