The hydrophobic properties of amino acid side chains were characterized on the basis of the partition process in the 1-octanol-water system. The partition coefficients were calculated from the published data and the distribution coefficients were determined experimentally on the basis of a double partition process utilizing the fact that the amino acids pass almost completely into the aqueous phase in the partition process. When the volumes of water and 1-octanol are suitably selected, this fact permits avoidance of the difficulties associated with the determination of amino acids in 1-octanol, where their solubilities are very low. Our scale is the only complete experimental scale based on the partition process of amino acids in the 1-octanol-water system. It follows from comparison of the calculated and the experimental data with the values published for the distribution coefficients of N-acetyl amides of amino acids that the best agreement was achieved for hydrophobic amino acids, while greater differences were observed for hydrophilic amino acids. These differences, expressed as the logarithm of the distribution coefficients, correspond to an average of 0.08 for nonpolar amino acids and 0.30 for acidic and basic amino acids: expressed as relative deviations, these values correspond to 2-10% for nonpolar amino acids, and 5-30% for charged amino acids.

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The mechanism of denaturation of human serum albumin by urea was examined by polarography, polarimetry, circular dichroism, UV-spectrophotometry, gel chromatography, and polyacrylamide gel electrophoresis. Comparison of the results obtained by these methods shows that this reaction is a complex process which cannot be described by a two-state denaturation model. It has been demonstrated that the different states which denaturation produces arise under different denaturation conditions. The different behavior of various species of human serum albumin (monomer, mercaptalbumin and nonmercaptalbumin) during denaturation by urea was examined. As a result the following probable denaturation scheme was proposed: The denaturation of human serum albumin by urea is regarded as a stepwise process involving one stable intermediary product at least ( demonstrated electrophoretically). After the rapid initial change of the ordered helical structure extensive hydrophobic domains of the molecule remain folded. Cystine residues are gradually liberated from these domains. Denaturated mercaptalbumin has the conformation of a random coil in which the pairing of native disulfide bonds has been altered because of SH-S-S interchange reactions; in contrast native disulfide bonds are retained in nonmercaptalbumin.

Analysis of the course of D-glucose binding to insulin has shown that the mechanism of glucose-insulin interaction is a cooperative process. Binding of D-glucose molecules to insulin is facilitated by the dissociation of insulin aggregates caused by insulin-glucose interaction. Thus, insulin behaves as a system with strong positive cooperativity. The results have been treated in accordance with theories for interactions coupled to association equilibria. The data obtained support the idea that insulin monomers are the active species responsible for insulin action.

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