[Mathematical modelling of charge properties of protein molecules]

A procedure of theoretical determination of the dependence of protein molecule charge on the medium pH has been developed. The suggested procedure allows calculating the protein pI value, the molecule charge at the definite pH value, as well as the corresponding values for the protein molecule. Calculations for insulin, apo A-I and apo A-II molecules have been carried out. Calculated pI values are equal to 5.25, 5.64 and 4.86, respectively. A comparison of the theoretical curves and experimental data allows obtaining information of the molecule structure. Carboxyl groups with abnormally high pK values are discovered, that, probably, indicates to the direct interaction of two COOH-groups. A supposition is made on the most probable arrangement of the functional fragments in apo A-I and apo A-II molecules.