Ethanol-induced conformational transitions in holo-α-lactalbumin: Spectral and calorimetric studies

Conformational transitions of holo-α-lactalbumin in a hydro-ethanolic cosolvent system was studied by spectrofluorescence, CD in near- and far-uv regions, and high-sensitivity differential scanning calorimetry. Experimental results allow us to propose that in isothermal conditions α-lactalbumin undergoes a number of conformational transitions with increasing ethanol concentration: N ⇔ I ⇔ D ⇔ H . The existence of I -state was deduced from spectrofluorometric and near-uv CD data. In this state the aromatic chromophores of the amino acid side chains are more accessible to the solvent displaying higher local mobility. The H -state was detected from far-uv CD spectra as a state corresponding to the content of α-helices higher than originally found in native protein. However, calorimetric measurements provide data revealing only the two-state mechanism of α-lactalbumin unfolding in both water and in aqueous ethanol solutions. This indicates that the energy levels of N - and I -states as well as of D - and H -states are similar. Thermodynamics of the unfolding of α-lactalbumin in hydro-ethanolic solutions was analyzed with the help of the linear model of solvent denaturation. Unfolding increments of enthalpy, entropy, and Gibbs energy of transfer of the protein from a reference aqueous solution to hydro-ethanolic solutions of different concentrations were determined from the calorimetric data. They are linear functions of molar ethanol fraction. The slope of the unfolding increment of Gibbs energy of transfer was calculated from data on transfer of amino acid residues taking into account the average solvent accessibility of amino acid residues in the native structure of small globular proteins, using the additive group contribution method. © 1998 John Wiley & Sons, Inc. Biopoly 46: 253–265, 1998     

Simultaneous activity of nucleolus organizer regions of human and Chinese hamster chromosomes in somatic cell hybrids

In an interspecific human-Chinese hamster hybrid that retains 13 and 85.6% of the chromosomes of each parental complement, activity of nucleolus-organizing regions (NOR) of both type chromosomes is observed in 18.9% of the cells. Interspecific chromosomal associations are also noted. Unlike the parental lines of Chinese hamster cells, the hybrids show the associations of the NOR of Chinese hamster chromosomes. In hybrid cells, there occurs partial suppression of NOR activity in human and Chinese hamster chromosomes, while the NOR of the 3d chromosome of the Chinese hamster is completely suppressed.     

Thermal sensitivity of enzymes in trisomy 21 leukocytes]

Thermosensitivity of glucose 6-phosphate dehydrogenase and myloperoxidase was investigated in the leukocyte lysates from patients with Down's syndrome. A statistically significant enhancement of thermosensitivity of both the enzymes investigated was revealed in the aberrant cells in comparison with the control. The noted differences can be based on the increased incidence of mutation injuries in the aberrant cells, as well as on anomalous postranslational modification of the protein molecules.     

Mathematical model of interphase cell death. Biophysical justification and generalization

The authors propose a biophysical justification of a radiation-induced injury and interphase death of cells. The injury to certain units of the microtrabecular network and cytoskeleton is considered to be a primary biological effect of radiation on cells. The role of these structural changes in the development of the specific radiation response is discussed. It is found possible to describe formally, by the defined parameters of the proposed model, the survival curves for not only interphase but also reproductive cell death.     

Study of lysozyme by a spin-label method in the 2-mm range

Two millimeter range ESR-spectroscopy was used to measure the values of magnetic resonance parameters of egg lysozyme samples modified with nitroxyl label 4-(iodine-acetamide)-2,2,6,6-tetramethylpiperidine-1-oxyl by hist-15 residue. It has been shown that in a lyophilic sample the spin label forms a hydrogen bond with the protein group and when the sample is moistened--with water molecules. Temperature changes of the pattern of ESR line are analysed. It is concluded that in the moistened samples within 230-320 K the nitroxyl fragment of the label gets engaged in anisotropic movement with preferable rotation around Z-axis of N-O. fragment with anisotropy coefficient 5 and mean correlation time tau congruent to 5 X 10(-7) divided by 5 X 10(-8) c.     

Two-way microscale interactions between immigrant bacteria and plant leaf microbiota as revealed by live imaging

The phyllosphere – the aerial parts of plants – is an important microbial habitat that is home to diverse microbial communities. The spatial organization of bacterial cells on leaf surfaces is non-random, and correlates with leaf microscopic features. Yet, the role of microscale interactions between bacterial cells therein is not well understood. Here, we ask how interactions between immigrant bacteria and resident microbiota affect the spatial organization of the combined community. By means of live imaging in a simplified in vitro system, we studied the spatial organization, at the micrometer scale, of the biocontrol agent Pseudomonas fluorescens A506 and the plant pathogen P. syringae B728a when introduced to pear and bean leaf microbiota (the corresponding native plants of these strains). We found significant co-localization of immigrant and resident microbial cells at distances of a few micrometers, for both strains. Interestingly, this co-localization was in part due to preferential attachment of microbiota cells near newly formed P. fluorescens aggregates. Our results indicate that two-way immigrant bacteria – resident microbiota interactions affect the microscale spatial organization of leaf microbiota, and possibly that of other surface-related microbial communities.Subject terms: Microbial ecology, Microbial ecology