Determination of sedimentation coefficients of subcellular particles of rat liver homogenates. A theoretical and experimental approach

A simple and convenient method is described for the determination of the average sedimentation coefficients ($\overline{S}?values$) of subcellular particles in a homogenous solution by velocity sedimentation in the preparative ultracentrifuge (swinging-bucket rotor). Theoretically the method is based on the distribution of intact organelles between sediment and supernatant and the convergence of their sedimentation at high centrifugal effects. The data have been treated according to the rate equation of parallel sedimentation in horizontal cylindrical tubes which has been converted to a linear function. By measuring activities of marker enzymes in the sediments, the theory has been confirmed experimentally in the determination of $\overline{S}?values$ and the distribution between supernatant and sediment of intact mitochondria, lysosomes and peroxisomes of rat liver homogenates. The effect of particle concentration on the $\overline{S}?values$ of mitochondria has been determined.     

Determination of Dynamical Heterogeneity from Dynamic Neutron Scattering of Proteins

Motional displacements of hydrogen (H) in proteins can be measured using incoherent neutron-scattering methods. These displacements can also be calculated numerically using data from molecular dynamics simulations. An enormous amount of data on the average mean-square motional displacement (MSD) of H as a function of protein temperature, hydration, and other conditions has been collected. H resides in a wide spectrum of sites in a protein. Some H are tightly bound to molecular chains, and the H motion is dictated by that of the chain. Other H are quite independent. As a result, there is a distribution of motions and MSDs of H within a protein that is denoted dynamical heterogeneity. The goal of this paper is to incorporate a distribution of MSDs into models of the H incoherent intermediate scattering function, $I\left(Q,t\right)$, that is calculated and observed. The aim is to contribute information on the distribution as well as on the average MSD from comparison of the models with simulations and experiment. For example, we find that simulations of $I\left(Q,t\right)$ in lysozyme are well reproduced if the distribution of MSDs is bimodal with two broad peaks rather than a single broad peak.     

Estimation of Parameters of Rotatory Dispersion Curves of Proteins

Estimation of the constants a, b, and λ₀ by means of the standard Moffitt-Yang plot is evaluated. It is found that the method is very insensitive as an estimation procedure and that large errors in b may be expected. Expressions for the maximum-likelihood estimates of the constants are derived.     

A microdosimetric analysis of the interactions of mono-energetic neutrons with human tissue

Nuclear reactions induced during high-energy radiotherapy produce secondary neutrons that, due to their carcinogenic potential, constitute an important risk for the development of iatrogenic cancer. Experimental and epidemiological findings indicate a marked energy dependence of neutron relative biological effectiveness (RBE) for carcinogenesis, but little is reported on its physical basis. While the exact mechanism of radiation carcinogenesis is yet to be fully elucidated, numerical microdosimetry can be used to predict the biological consequences of a given irradiation based on its microscopic pattern of energy depositions. Building on recent studies, this work investigated the physics underlying neutron RBE by using the microdosimetric quantity dose-mean lineal energy $\left({\bar{y}}_D\right)$ as a proxy. A simulation pipeline was constructed to explicitly calculate the ${\bar{y}}_D$ of radiation fields that consisted of (i) the open source Monte Carlo toolkit Geant4, (ii) its radiobiological extension Geant4-DNA, and (iii) a weighted track-sampling algorithm. This approach was used to study mono-energetic neutrons with initial kinetic energies between 1 eV and 10 MeV at multiple depths in a tissue-equivalent phantom. Spherical sampling volumes with diameters between 2 nm and 1 $\mathrm{\mu }$m were considered. To obtain a measure of RBE, the neutron ${\bar{y}}_D$ values were divided by those of 250 keV X-rays that were calculated in the same way. Qualitative agreement was found with published radiation protection factors and simulation data, allowing for the dependencies of neutron RBE on depth and energy to be discussed in the context of the neutron interaction cross sections and secondary particle distributions in human tissue.     

Familial Correlations of the Ages of Manifestation of Lung Cancer and Large-Intestine Cancer

The probability to develop lung cancer before 80 years of age is 1.67 and 0.18% for the male and female populations of Kharkov, respectively; the probability to develop large-intestine cancer is 0.92 and 0.49%, respectively. The correlation coefficient (r) of the age of manifestation (AM) of cancer in parent–offspring pairs is 0.47. These correlation coefficients for the father–son, mother–daughter, mother–son, and father–daughter pairs are 0.64, 0.49, 0.44, and 0.37, respectively. If the parent has lung cancer, the correlation is stronger (r = 0.71). On average, cancer is manifested in offspring earlier than in parents (57 and 63 years, respectively); the differences in the father–daughter and mother–son pairs are 8.2 and 2.8 years, respectively. The best prognostic parameter is the AM of cancer in the father with respect to the AM in the son (b _yx = 0.45).     

Analysis of morphogenetic mutants of hydra

Summary A mutant ofHydra attenuata is analysed, theaberrant, which is distinct from the wild type in having a smaller head with fewer tentacles and only half the number of head-specific cells. The rate of head and foot regeneration and the doubling time are slower inaberrants than in normal hydra.The lower head-forming potential is paralleled by a reduced concentration of head-specific morphogens: compared to the wild type, in theaberrant the concentration of head activator is reduced to 70% in the head and to 50% in the body, the concentration of head inhibitor is reduced to 50% in the head and to 80% in the body. Theaberrant is more sensitive (3 times) to added head activator and less sensitive (>5 times) to added head inhibitor than the wild type.The slower rate of foot regeneration is paralleled by a lower content of foot-specific morphogens: compared to the wild type, in theaberrant the foot activator is reduced to 40% and the foot inhibitor to 70%.     

Role of carbon dioxide in germination of spores of Streptomyces viridochromogenes

CO₂ in required continuously during germination of Streptomyces viridochromogenes spores. Spores incubated in a defined germination medium in the absence of CO₂ remain phase bright and do not release spore carbon. In the presence of CO₂, the spores initiate germination accompanied by loss of refractility and spore carbon. The CO₂ requirement is replaced by oxaloacetate or a mixture of tricarboxylic acid cycle (TCA) intermediates. Labeled CO₂ is taken up by germinating spores, and is incorporated into protein and RNA. TCA cycle intermediates and related amino acids contain most of the acid-soluble label following short term exposures of germinating spores to ¹⁴CO₂. TCA cycle inhibitors repress germination and ¹⁴CO₂ uptake whereas folic acid antagonists do not. The results indicate that CO₂ is incorporated into oxaloacetate which is converted to biosynthetic intermediates required for germination. Operation of the TCA cycle appears to be essential for spore germination. The conclusion is reached that CO₂ is required during germination in order to maintain the cycle by an anaplerotic reaction.Abbreviations SN sucrose-nitrate medium - TX buffer Trisbuffer pH 7.3 containing-Triton X-100 - DGM defined germination medium - TX salts TX buffer plus Mg and Ca ions - TA trichloroacctic acid - TCA tricarboxylic acid     

Spores of microorganisms

Preexisting¹⁴C-DAP in vegetative cells ofBacillus cereus is not incorporated into the spores, but is released into the medium after sporogenesis is complete. Exogenous¹⁴C-DAP added to the medium before sporulation is incorporated intensively into the sporangia and practically all of it is taken up by the spores. During sporogenesis, two periods of increased incorporation of¹⁴C into hot TCA-precipitate of cells are found after adding¹⁴C-DAP— one before formation of the spores, when¹⁴C-lysine formed by decarboxylation is incorporated together with¹⁴C-DAP, and one during the “whitening” phase, when any¹⁴C-lysine is no longer incorporated. The incorporation of exogenous¹⁴C-lysine into the sporangial proteins is also markedly elevated during the presporulation phase and at the outset of sporogenesis.     

The effect of sterols on the metabolism of Pythium species

Summary The growth of several Pythium species is increased between 65 and 100% if cholesterol is added to the growth medium. The optimum concentration is 15 mcg per ml. Mycelium of Pythium ultimum, in which cholesterol is present, incorporates glucose-U-¹⁴C and releases ¹⁴CO₂ at a faster rate than the corresponding sterol free mycelium. In sterol containing cells, more ¹⁴CO₂ is produced from a given amount of absorbed glucose-U-¹⁴C than in sterol free cells, there is thus in sterol containing hyphae a higher level of energy production. This condition can account for the increase in growth due to cholesterol. Only if sterols are present in the cellular membranes of Pythium species is the optimum synthetic capacity reached.