Role of temperate phage in bacterial dissociation

The analysis of literary and own data testifies that the dissociants may appear in bacteria population from spontaneous mutations and transfer of genetic material (conjugation, transformation, transduction). The phage conversion and different DNA reorganizations within a cell where prophage plays an active role, probably introduce the largest contribution into the dissociative transitions of variants which occur with high frequency (about 10(-2)-10(-4). The dissociation of various bacteria has been studied with different degree. The role of temperate phage has been shown in splitting of bacteria into variants in the genera Mycobacterium, Corynebacterium, some Bacillus, Clostridium, Staphylococcus, some enterobacteria, Yersinia, Vibrio Pseudomonas, Rhizobium, Nostoc; the participation of prophage in dissociation of bacteria of the genera Xanthomonas, Erwinia, Bacteroides is proposed. A method for obtaining the nondissociating S-variants for stability of biologically active substances synthesized by cells has been suggested.     

Dissociation of mitochondrial ribosomes of neurospora crassa by a bacterial dissociation factor

From ribosomes of Escherichia coli a protein factor can be obtained that promotes dissociation of bacterial ribosomes into subunits. Incubation of mitochondrial ribosomes from Neurospora crassa with the bacterial dissociation factor also leads to the formation of subunits. Under the same conditions no dissociation of cytoplasmic ribosomes from Neurospora crassa was observed.     

On the dissociation constants of BAPTA-type calcium buffers

We have determined or redetermined the calcium dissociation constants of seven BAPTA-type buffers with KD's in the range from 0.4 microM to about 20 mM in 300 mM KCl. These include four newly synthesized ones: 5-nitro BAPTA; 5,5'-dinitro BAPTA; 5-methyl-5'-nitro BAPTA; and 5-methyl-5'-formyl BAPTA. Moreover, we tabulate dissociation constants or KD's for BAPTA and eleven BAPTA-type buffers, compare most of them with an empirical curve based upon so-called Hammett values, and predict KD's for several still unsynthesized but potentially valuable buffers.     

On the reality of transition state dissociation constants

Transition state dissociation constants are currently considered, utilizing stopped flow equipment. The underlying theory is briefly reviewed, relating the ideas to steady state kinetics of enzyme systems. The ideas are further analyzed under the consideration of chemical relaxation. Test conditions are described which would allow an investigation of the concepts of transition state dissociation constants by chemical relaxation techniques. A discussion concerning the way in which the concepts of transition state dissociation constants relate to other theories which assume short-lived, but real, dissociation constants is included. The theory is rigorously analyzed (in a second part), revealing the nature of the assumption of a transition state dissociation constant: While they may be written in a formal manner, they are not based on reality—on kinetic grounds direct interconversions between transition states are practically impossible. This applies also to transition state dissociation constants involving protons.     

Structural dynamics of bacterial ribosomes: V. Magnesium-dependent dissociation of tight couples into subunits: Measurements of dissociation constants and exchange rates

The magnesium ion-dependent equilibrium of vacant ribosome couples with their subunits

$\text{70}\text{S}\text{?}\text{k}{}_{\mathrm{?1}}\text{k}{}_1\text{50}\text{S}\text{+30}\text{S}$

has been studied quantitatively with a novel equilibrium displacement labeling method which is more sensitive and precise than light-scattering. At a concentration of 10^?7m, tight couples (ribosomes most active in protein synthesis) dissociate between 1 and 3 mm-Mg²⁺ at 37 °C with a 50% point at 1.9 mm. The corresponding association constants K_a′ are 5.1 × 10⁵m^?1 (1 mm-Mg²⁺), 3.5 × 10⁷m^?1 (2 mm), and 1.2 × 10⁹m^?1 (3 mm), about five orders of magnitude higher than the K_a′ value of loose couples studied by Spirin et al. (1971) and Zitomer & Flaks (1972).In this range of Mg²⁺ concentrations ($\text{37 °C, 50 mm-}\text{NH}{}_4{}^{\mathrm{+}}$) the rate constants depend exponentially and in opposite ways on the Mg²⁺ concentration: k₁ = 2.2 × 10^?3s^?1, k_?1 = 7.7 × 10⁴m^?1s^?1 (2mm-Mg²⁺); k₁ = 1.5 × 10^?4s^?1, k_?1 = 1.7 × 10⁷m^?1s^?1 (5 mm-Mg²⁺). Under physiological conditions (Mg²⁺ ～- 4 mm, ribosome concn ～- 10^?7m), the equilibrium strongly favors association and the rate of exchange is slow ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{～- 10}\text{min}$). In the range of dissociation (2 mm-Mg²⁺), association of subunits proceeds without measurable entropy change and hence ΔG^O = ΔH^O. The negative enthalpy change of ΔH^O = ? 10 kcal suggests that association of subunits involves a shape change.Below a critical Mg²⁺ concentration (～- 2 mm), the 50 S subunits are converted irreversibly into the b-form responsible for the transition to loose couples. The results are compatible with two classes of binding sites, one class binding Mg²⁺ non-co-operatively and contributing to the free energy of association by reduction of electrostatic repulsion, and another class probably consisting of hydrogen bonds between components at opposite interfaces whose critical spatial alignment rapidly denatures in the absence of stabilizing magnesium ions.     

Evidence for fast conformational change upon ligand dissociation in the HemAT class of bacterial oxygen sensors

Here we report the results of transient absorption and photoacoustic calorimetry studies of CO photodissociation from the heme domain of the bacterial oxygen sensor HemAT-Bs. The results indicate that CO photolysis is accompanied by an overall DeltaH of -19 kcal mol(-1) and DeltaV of +4 ml mol(-1) as well as a red-shifted kinetic difference spectrum all occurring in <50 ns. Analysis of the DeltaH/DeltaV reveals that a conformational change takes place with a DeltaH(conf) of -40 kcal mol(-1) and DeltaV(conf) of -22 ml mol(-1). These thermodynamic changes are consistent with an increase in the solvent accessible surface area of the protein upon ligand dissociation, as observed in the X-ray structure of the ferric CN-bound and CN free forms of HemAT-Bs.     

Protein complexes in bacterial and yeast mitochondrial membranes differ in their sensitivity towards dissociation by SDS

Previously, a 2D gel electrophoresis approach was developed for the Escherichia coli inner membrane, which detects membrane protein complexes that are stable in sodium dodecyl sulfate (SDS) at room temperature, and dissociate under the influence of trifluoroethanol [R. E. Spelbrink et al., J. Biol. Chem. 280 (2005), 28742-8]. Here, the method was applied to the evolutionarily related mitochondrial inner membrane that was isolated from the yeast Saccharomyces cerevisiae. Surprisingly, only very few proteins were found to be dissociated by trifluoroethanol of which Lpd1p, a component of multiple protein complexes localized in the mitochondrial matrix, is the most prominent. Usage of either milder or more stringent conditions did not yield any additional proteins that were released by fluorinated alcohols. This strongly suggests that membrane protein complexes in yeast are less stable in SDS solution than their E. coli counterparts, which might be due to the overall reduced hydrophobicity of mitochondrial transmembrane proteins.     

On the bacterial degradation of lignin

Summary Several bacteria which can degrade numerous phenols with structural relationships to lignin were tested for their ability to degrade lignin. The biodegradation with all the tested bacteria was poor. The method of lignin extraction, presence of glucose as cosubstrate and changes in the nitrogen source of the medium did not affect the extent of lignin degradation. The poor degradation does not seem to be influenced by medium composition and culture condition but is more probably due to the inability of the tested bacteria to degrade lignin to any considerable extent.     

On the adaptive nature of the dissociation process in Bacillus thuringiensis

The process of dissociation into variants differing in colony morphology occurring in batch cloned cultures of two Bacillus thuringiensis strains belonging to different subspecies was studied at optimal and elevated temperatures. An increase in the cultivation temperature to 40 degrees C resulted in an increase in the fraction of R variants to 100% after 72 h of cultivation of either of the strains. This increase was not due to the selection of forms with greater resistance to elevated temperature. The level of resistance to elevated temperature was determined by the strain genotype and did not correlate with morphological characteristics of the colonies.     

On the dissociation of the cytochrome b-c1 of potato mitochondria

Potato tuber mitochondria, depleted from cytochrome c by salt washing, were dispersed by bile salts to obtain a soluble fraction containing the cytochrome b-c₁ complex. The dissociation of this complex was only possible by using β-mercaptoethanol and seems to involve the disappearance of 2 of the 3 b cytochromes seen in plant mitochondria and in the soluble b-c₁ complex. Spectral characteristics of the isolated cytochromes b and c₁ are given.     

On the biosynthesis of bacterial ribosomal RNA

By comparison of the fingerprints of 5S and 23S ribosomal RNAs from Bacillus licheniformis with that of the precursor of 23S ribosomal RNA, it can be shown that 5S RNA is not a part of the precursor of 23S ribosomal RNA.