[Kinetics of interaction between apomyoglobin and phospholipid membrane].

The interaction of apomyoglobin and its mutant forms with phospholipid membranes was studied using tryptophan fluorescence and CD in the far UV-region. It is shown that a negatively charged phospholipid membrane can have a double effect on the structure of protein molecule upon their interaction: it denatures the native structure of the protein to its intermediate state similar to that in solution, acting as a moderately denaturing reagent. On the other hand, it can structure the unfolded protein to the same intermediate state stabilizing its structure. The kinetics of interaction between the protein and its mutant forms and the phospholipid membrane depends on the charge of the membrane surface. Here the rate of this interaction depends on the phospholipids vesicle concentration and the protein molecule stability increasing with a decrease of the latter. The importance of the obtained results for the folding of membrane proteins and the choice of the pathway for target delivery of protein drugs are discussed.

[Investigation of apomyoglobin stability depending on urea and temperature at two different pH values].

Equilibrium unfolding of apomyoglobin by urea was investigated in the temperature range from 5 to 25 degrees C at two pH values. The thermodynamic parameters of the apomyoglobin native-unfolded state transition were determined. Conformational changes in the protein structure were monitored by tryptophan fluorescence and far UV circular dichroism. Apomyoglobin preserves its native conformation at pH 5.7 and 6.2 in the temperature range used. It was shown that the apomyoglobin stability and its unfolding cooperativity are substantially lower at 5 degrees C than at other temperatures. This fact should be taken in account at the investigation of apomyoglobin.

[Conformational states of the water-soluble fragment of cytochrome b5. I. pH-induced denaturation]. / Konformatsionnye sostoianiia vodorastvorimogo fragmenta tsitokhroma b5. I. pH-zavisimaia denaturatsiia.

Cytochrome b5 is a membrane protein that comprises two fragments: one is water-soluble and heme-containing, and the other is hydrophobic and membrane-embedded. The function of electron transfer is performed by the former whose crystal structure is known; however, its conformational states when in the membrane field and interacting with other proteins are still to be studied. Previously, we proposed water-alcohol mixtures for modeling the effect of membrane surface on proteins, and used this approach to study the conformational behavior of positively charged cytochrome c as well as relatively neutral retinol-binding protein also functioning in the field of negatively charged membrane. The current study describes the conformational behavior of the negatively charged water-soluble fragment of cytochrome b5 as dependent on pH. Decreasing pH was shown to transform the fragment state from native to intermediate, similar to the molten globule reported earlier for other proteins in aqueous solutions: at pH 3.0, the fragment preserved a pronounced secondary structure and compactness but lost its rigid tertiary structure. A possible role of this intermediate state in cytochrome b5 functioning is discussed.