The in situ spatial arrangement of the influenza A virus matrix protein M1 assessed by tritium bombardment.

Intact influenza A virions were bombarded with thermally activated tritium atoms, and the intramolecular distribution of the label in the matrix protein M1 was analyzed to determine the in situ accessibility of its tryptic fragments. These data were combined with the previously reported x-ray crystal structure of the M1 fragment 2-158 [Sha, B. & Luo, M. (1997) Nat. Struct. Biol. 4, 239-244] and the predicted topology of the C domain (159-252) to propose a model of M1 arrangement in the virus particle.

Determination of the accessible surface of globular proteins by means of tritium planigraphy.

Results are presented for proteins with known three-dimensional structure (lysozyme, myoglobin, ribonuclease), which show that the probability of label incorporation upon bombardment by "hot" tritium atoms may be quantitatively linked with the surface area of the protein accessible to water molecules. Possible deviations from simple linear dependency caused by particular mechanisms of label introduction are discussed. The data obtained in experiments with model systems were used to determine the accessible surface area of human serum albumin, for which structural data is not sufficiently accurate to allow estimation of accessible surface area. Experimental data correlate reasonably well with estimations based on conventional concepts of the relationship between accessible surface area and molecular weight for globular proteins.

On inherited fertility in biological systems: a model of correlated fluctuations in the stochastic branching process.

A new evolutionary model with hereditary modes considered as correlated fluctuations of fertility has been proposed. It has been demonstrated that the model allows the global statistical properties of the system to be evaluated, e.g. the ensemble average and the probability of extinction. The results obtained show the increase of instability of a population with the enhancement of inheritance efficiency. The existence of at least an exponential stratification in the population has also been shown. Possible applications of the present model are discussed.

Handedness, origin of life and evolution.

Biological polymers have a preferred chirality ond can replicate themselves. Physical arguments provide insight into which of these unique and apparently related properties evolved first, and by what mechanism.

Homochirality and stereospecific activity: evolutionary aspects.

The problem discussed in this paper is the connection between the unique property of biopolymers (proteins, DNA and RNA), i.e. homochirality, and their main functional property, i.e. self-replication. Our approach is based on an analysis of the conditions for the origination of the mechanism of self-replication of chiral polymers. It is demonstrated that self-replication could originate only on the basis of homochiral structures, possessing stereospecific (enzymatic) activity. It is also shown that complete breaking of the mirror symmetry of the organic medium is required both at the stage of polymeric takeover and at the stage of formation of structures possessing stereospecific activity. This requirement is satisfied only in the framework of the mechanism of spontaneous symmetry breaking i.e. the mechanism of non-equilibrium phase transition from the racemic state of the organic medium to the chirally pure one. The results obtained suggest that homochirality is a necessary condition for the origination of biological specificity and plays a fundamental role in the formation of structures capable of self-replication.

Hemoglobin dynamics in rat erythrocytes investigated by Mössbauer spectroscopy.

Rats have been enriched in 57Fe and erythrocytes were isolated from the blood. Mössbauer absorption spectroscopy on the hemoglobin of these erythrocytes has shown rather similar dynamics as found earlier in crystals of myoglobin, in frozen solutions of human hemoglobin and in a number of other proteins. The results strongly indicate that the motion of the heme and presumably some part of the F-helix is mainly influenced by the average viscosity of the sample determined by a network of hydrogen bridges and other weak interactions. Extrapolations of Mössbauer results from protein crystals to proteins in their physiological surroundings seem to be suitable for heme proteins.

The use of thermally activated tritium atoms for structural-biological investigations: the topography of the TMV protein-accessible surface of the virus.

Thermally activated tritium atoms were used for studying the topography of the TMV protein-accessible surface of the virus. The accessibility profile of amino acid residues in a protein polypeptide chain was determined from data on the intramolecular distribution of a tritium label in the TMV protein. It was shown that tryptic peptides T3, T4, T12, the N-terminal region of peptide T1 and the proximal tryptic peptide T8 (located 20 to 25 A (1 A = 0.1 nm) from the viral axis) are accessible to tritium labelling. The fact of tritiation of the viral RNA was detected as well. This evidence was compared with the high-resolution X-ray analysis data for the TMV. A model is suggested to explain the exposure of the buried sites of the virus to thermally activated tritium atoms. The possibilities and limitations of this method in studying the surface topography of proteins in supramolecular systems as well as for location of protein antigenic regions are discussed.

Chiral purity of nucleotides as a necessary condition of complementarity.

This work discusses the question about the role of chiral purity (homochirality) of nucleotides in the formation of complementary replicas. A qualitative answer to this question can be obtained from molecular models constructed to simulate the chiral defect in the polynucleotidic chain. It shows the necessity of homochirality of nucleotides for the complementarity preservation. The necessity of the strong mirror-symmetry breaking in the abiogenic formation of the self-replicating oligonucleotide structures is discussed in the context of prebiological evolution.

Investigation of large intramolecular movement within metmyoglobin by Rayleigh scattering of Mössbauer radiation (RSMR).

This paper reports Rayleigh scattering experiments on metmyoglobin crystals and freeze dried myoglobin which was exposed to air with different parital pressure of water vapor. While dry myoglobin shows no fluctuations between conformational substates such "breathing modes" are rarely seen in water covered myoglobin. Larger amounts of water increase the average mean square displacements. In crystals the dynamic behaviour is hindered by the crystal packing. The results are analysed by a theory describing the motion within the molecule by a Langevin equation with restoring forces corresponding to a square well potential.

Electron tunneling process and the segment mobility of macromolecules.

New experimental data [Berg, A. I., Noks, P. P., Kononenko, A. A., Frolov, E. N., Khrymova, I. N., Rubin A. B., Likhtenstein, G. I., Goldanskii, V. I., Parak, F., Bukl, M. & Mössbauer, R. (1979) Mol. Biol. (USSR) 13, 81-89; Berg, A. I., Noks, P. P., Kononenko, A. A., Frolov, E. N., Uspenskaya, N. Y., Khrymova, I. N., Rubin, A. B., Likhtenstein, G. I. & Hideg, K. (1979) Mol. Biol (USSR) 13, 469-477] provide evidence that the electron tunneling process is connected to a special type of conformational transition (segmental transition) protein macromolecules in photosynthetic membranes. This problem is investigated with a simple mechanical model. It is shown that the segmental degree of freedom can play the role of the strongly interacting accepting mode for the electron tunneling process. The temperature dependences of the electron tunneling rate and the recoilless gamma-ray absorption of membrane-bound 57Fe, as an indicator of the intramolecular mobility, are calculated. The problem of energy storage in proteins is also discussed.

Quantum low-temperature limit of a chemical reaction rate.

The radiation-induced polymerization of formaldehyde has been studied in the solid state. The time of addition of one new link to a polymer chain increases exponentially in accordance with the Arrhenius law at 140 to 80 K, but approaches a constant value (approximately 10(-2) second) at temperatures below 10 K. Thus, a low-temperature limit to a chemical reaction rate has been observed. It is interpreted as a quantum effect caused by tunneling from the zero vibration level of the initial state, and a semiquantitative theory is given. The phenomenon should be taken into account for understanding tunneling of electrons in biological systems when such tunneling is accompanied by conformational changes. It could also be significant in slow, exothermic chemical reactions at low and ultralow temperatures, which may have had a role in chemical and biological evolution (cold prehistory of life?).