Some constituents of Pitavia punctata

Extracts from the stems and leaves of Pitavia punctata Mol. were examined. The neutral fraction yielded β-sitosterol, daucosterin, quercetin, avicularin, and the previously undescribed quercetin 3-rhamnosylarabinoside. Braylin was co-extracted with the basic constituents, dictamnine, skimmianine and γ-fagarine. Acid hydrolysis of the leaves yielded cyanidin and delphinidin.     

A biochemical and stereological study of neonatal rat hepatocyte subpopulations. Effect of pre- and postnatal exposure to ethanol

Hepatocytes from 12-day-old rats, pre- and post-natally exposed to alcohol, together with those from pair-fed controls, were isolated and subfractionated in six cell subpopulations on Percoll density gradients. These cells were characterized using a combination of biochemical and stereological methods. The low density cells (F2) mainly showed biochemical and stereological features of perivenous hepatocytes, whereas the heavier cells (F6) were primarily periportal hepatocytes. The alcohol-metabolizing enzymes, alcohol dehydrogenase and aldehyde dehydrogenase (high and low Km) showed more activity in the F2 fraction. Alcohol-altered mitochondria and Golgi apparatus occurred mainly in F2 cells, whereas the endoplasmic reticulum and lysosomes appeared to be more altered in the F6 hepatocytes. Alcohol also induced the appearance of some small hepatocytes, with a well-developed rough endoplasmic reticulum and an increased number of mitochondria. Biochemical data indicated that glutamate dehydrogenase and alanine aminotransferase were more affected in F2 cells from alcohol-treated rats, and that the activity of the ethanol-metabolizing enzymes was alos reduced in these hepatocytes. Our results indicate that alcohol exposure during zonal development in the liver could have a selective effect on specific cell components depending on the acinar zone, and that the perivenous hepatocytes appear to be more damaged under these conditions.     

On the toroidal condensed state of closed circular DNA

The influence of double helix torsional elasticity on the compaction and structure of circular DNA compact form is studied theoretically in the case when the compact (globular) form has torus shape. For closed circular DNA the topological invariant, the linking number, yields a strict connection between conformation of the double helix considered as unifilar homopolymer and elastic energy of torsional twisting. The contribution of torsional elasticity to the free energy of the toruslike globule is calculated. This contribution is shown to be proportional to the square of superhelical density. Allowance of the torsional elasticity decreases the equilibrium radius of the toruslike globule formed by circular DNA. Closure of linear DNA into a ring widens the stability range of the relatively short DNA compact form and tightens it for long DNA.     

Measurement of spontaneous and X-irradiation-induced 6-thioguanine-resistant human blood lymphocytes using a T-cell cloning technique

Lymphocytes separated from human peripheral blood were cultured in vitro, in the presence of 6-thioguanine (TG), to select and clone rare TG-resistant (TGr) cells present in the circulation in vivo. The incidence of such TGr cells ranged from 0.83 X 10(-5) to 2.53 X 10(-5) (mean 1.48 X 10(-5) ) in healthy individuals aged between 19 and 79 years; did not differ between males and females; but increased significantly with age at a rate of 2.4 cells/10(7) lymphocytes/year. Exposure of lymphocytes (G0) in vitro to X-ray doses of upto 200 rad resulted in a dose-dependent increase in TGr cell frequencies. The rates of increase were approximately in proportion to the square of the dose and these rates were closely similar to those obtained in cultured skin fibroblasts and suggest that the bulk of these mutations are a consequence of chromosome structural aberrations. The cloned TGr cells are considered to be HPRT- mutants and the mutation frequencies in lymphocytes determined using this cloning technique were compared with the variant frequencies obtained in earlier experiments utilising an autoradiographic technique to detect azaguanine-resistant (AGr) variant cells. Mutation frequencies with the cloning technique were 10-20-fold lower than variant frequencies with the autoradiographic method.     

The phosphate diester linkage of the peptidoglycan polysaccharide moieties of Micrococcus lysodeikticus cell wall

The external polysaccharide is a major component of Micrococcus lysodeikticus cell wall and displays distinct composition. The complete structure of the external polysaccharide had been elucidated as a basis for investigation of the cell wall structure-function relation. However, the mode of attachment of the polysaccharide to the peptidoglycan through a phosphodiester was not clear due to limitations in structural and biosynthetic studies. The present study describes purification of a lysozyme-resistant nondialyzable high-molecular-weight fragment of cell wall and identifies the sugar, D-glucose, as the point of external polysaccharide attachment to the peptidoglycan through a phosphate diester. Kinetic studies for the acid-catalyzed release of external polysaccharide from the peptidoglycan were performed in parallel with synthetic [methyl-2-acetamido-3-O-(D-1-carboxyethyl)-2-deoxy-alpha-D- glucopyranoside-6-yl]-alpha-D-glucopyranosyl phosphate and alpha-D-glucopyranosyl phosphate and showed the presence of a phosphodiester linkage between external polysaccharide and peptidoglycan. In addition, type of phosphate residue and cross-linking between muramic acid and protein part have been determined.     

Detection of structural defects in phosphatidylcholine membranes by small-angle neutron scattering. The cluster model of a lipid bilayer

The oriented DPPC multilayers hydrated by D2O have been studied by a small-angle neutron scattering method in the Guinier range, and the gyration radius of the structural inhomogeneities has been estimated at about 29 A. They are interpreted as the annular defects between adjacent clusters uniting the all-trans chain 'segments' adjacent to the polar head group regions. The angle of the 'segment' tilt is determined by the hydrated polar group area (59.2 A2 for DPPC bilayers) and has been estimated to be about 44 degrees under the given experimental conditions. The hydrocarbon interior of a bilayer can be suggested as a 'sandwich' that is formed by two clustered layers (approx. 7 A of the thickness) and the central disordered (liquid) layer. The average cluster size along the bilayer surface is estimated to be approx. 24 A which correlates with the estimations of the short order region dimensions from the halfwidth of the X-ray 'packing' reflex (4.6 A)-1. The average interchain separation of approx. 5 A and the average cross-section area of a chain in a cluster (21.4 A2) were estimated from the reflex position and the chain cross-section geometry. The total volume of defects and the fraction of a bilayer surface occupied by them were estimated too.