TRITIUM PLANIGRAPHY OF BIOLOGICAL-SYSTEMS - PRINCIPLES OF THE METHOD AND A MATHEMATICAL-MODEL

In studying the surface of biological macromolecules by tritium planig raphy, the data obtained usuallY are correlated with the results of ca lculating the accessible surface by the Lee-Richards algorithm (for ob jects of known spatial structure). Therewith the fundamental differenc es between the model taken as the basis for calculations and the mecha nism of tritium label incorporation are completely ignored. In the pre sent work a new algorithm is proposed for calculating the accessible s urface area that more adequately reflects the specific conditions of t he chemical reactions taking place on the surface of a biological obje ct bombarded with atomic tritium. The best agreement between the calcu lations and the experimental data was achieved for an effective radius of the testing probe of 1.1 angstrom. Estimates were obtained for the probabilities of interaction between atomic tritium and amino acid re sidues, normalized over the accessible surface area. The accessible su rface area of the first 20 N-terminal residues of sperm whale myoglobi n is calculated according to the proposed model and to the Lee-Richard s algorithm for water molecules. The results of these calculations are shown to be appreciably different.