Influence of serum proteins on conformation of prostate-specific antigen.

Partition behavior of prostate-specific antigen (PSA) was studied in aqueous Dextran-Ficoll two-phase system. It was found that the partitioning of PSA changed in the presence of other proteins, in particular, bovine serum albumin, human serum albumin, human transferrin, and human gamma-globulin. The partition coefficient of PSA in mixtures with increasing amounts of these proteins decreased along the S-shaped curve and dropped to essentially the same value at the 10(4)-10(5) protein: PSA molar ratio. Partition behavior of the above proteins was examined separately. Partition coefficient of a protein represents the protein solvent exposed residues; i.e., it reflects the 3D-structure of the protein in solution. Partition of binary protein mixtures reflects the interaction of the two proteins and therefore characterizes the PSA-induced conformational changes in a protein agent and the change in the PSA conformation induced by a protein agent. In other words, the protein effect on the partition behavior of free PSA may be explained by the effect of the non-specific PSA-protein interactions on PSA conformation. Formation of such PSA-protein encounter complexes was shown to be dominated by the electrostatic forces, since the efficiency of a given protein-agent to induce changes in the partition behavior of PSA was proportional to its absolute mean net charge. Furthermore, in agreement with the earlier hypothesis that the protein segments with increased dynamic propensities (i.e., 'discrete breathers') can be important for conformational transitions accompanying binding processes, our analysis of intrinsically disordered regions (IDR) in all the proteins examined showed that the propensity for intrinsic disorder is related to the PSA partition-modulating capability of the protein.

Effect of thermal denaturation on vanillin binding to some food proteins.

Interactions of food proteins--beta-lactoglobulin (BLG), bovine serum albumin (BSA) und ovalbumin (OA)--with vanillin and effect of thermal denaturation of the proteins on vanillin binding were studies by US-VIS spectrophotometry. This method has its origin in characteristic changes in the vanillin absorption spectrum at vanillin-protein complex formation and allows to calculate concentrations of the bound and free ligand in aqueous solutions. Thermodynamic parameters, the intrinsic association constants and the number of binding sites of the vanillin binding to the native and thermodenaturated proteins (monomers and clusters) were determined. It is shown that the vanillin affinity for the native proteins is decreased in the following order: BSA > BLG > OA. This sequence is reversed for the protein thermoclusters. The stepwise annealing allowing to derive complex protein mixtures composed of different types of the native and denatured protein mixtures composed of different types of the native and denatured protein particles was applied to thermodenaturation of BSA. The vanillin affinity for BSA is decreased in the order: native protein > denaturated monomer > denaturated clusters. Vanillin interaction with the proteins is mainly electrostatic in nature.

[Effect of the molecular structure of natural anthracycline antibiotics on their relative hydrophobicity]. / Vliianie molekuliarnoi struktury prirodnykh antratsiklinovykh antibiotikov na ikh otnositel'nuiu gidrofobnost'.

Relative hydrophobicities of anthracycline antibiotics, adriamycin, rubomycin and carminomycin, have been measured by the two-phase distribution method. Two different biphasic systems were used for this purpose. Possible reasons of discrepancies between results obtained and other authors, data are discussed. It was established that the relative hydrophobicities of the compounds investigated contradict the theory of increment additivity. The results are compared with quantum-chemical calculations.