DISTRIBUTIONS OF THE USE FREQUENCIES OF AMINO-ACIDS IN THE HYPERVARIABLE REGIONS OF IMMUNOGLOBULINS

Two types of distributions for the frequencies of occurrence of amino acids in each position of hypervariable regions CDR-1 and CDR-2 were o btained for 2,000 immunoglobulins. The results show that some position s fit an inverse power-law distribution, while others fit an exponenti al-type distribution. As a result of comparison with structural data i n the literature it is proposed that sites in which the frequency dist ribution fits the inverse power law are critical to maintaining canoni cal shapes of the recognition regions or are involved in modulating th ese canonical conformations, while those sites where the distribution fits the exponential law are those which should be exclusively involve d in the recognition mechanism.