Liposome-cell interactions. A rapid assay for cells in suspension culture

A method has been developed for the rapid separation of cells in suspension from non-cell associated lipid vesicles in various assays for vesicle-cell interaction. Separation is achieved on a discontinuous Ficoll-Paque gradient. Cells and free vesicles are totally separated, as evidenced by both radiolabelled vesicles, and vesicles containing the fluorescent dye 6-carboxyfluorescein. The main advantages of this method are the rapidity, efficacy, and gentleness of the separation. Viability of the cells remains consistently high (greater than 96%) throughout the separation. Since this method involves a one-step centrifugation, it precludes the necessity for repeated washings of cells which have been incubated with lipid vesicles.     

On the mechanism of aging in soybean seeds

Changes in seeds of soybeans (Glycine max [L.] Merr. var. Wayne) which occur during accelerated aging (41 C, 100% relative humidity) showed subsequent loss of vigor, a decline in early respiratory activity, increased leakage of electrolytes, losses of as much as 10% dry weight from imbibing cotyledons, and a decrease in the swelling response of the imbibing system (seed plus H₂O). Each of these changes with aging is interpreted as resulting from deteriorative changes in membranes.     

Xeroderma pigmentosum endonuclease complexes show reduced activity on and affinity for psoralen cross-linked nucleosomal DNA.

Two DNA endonuclease complexes have been isolated from the chromatin of normal human and xeroderma pigmentosum, complementation group A (XPA), lymphoblastoid cells which are active on DNA damaged with psoralen plus long wavelength ultraviolet radiation (UVA). In both normal and XPA cells, one endonuclease complex, pI 4.6, recognizes the psoralen cross-link and the other endonuclease complex, pI 7.6, recognizes the psoralen monoadduct. The levels of activity of these complexes from both normal and XPA cells are similar on damaged naked DNA. Kinetic analysis of assays using graduated concentrations of substrate revealed that selective activity of these endonuclease complexes on 8-MOP plus UVA treated DNA correlates with a reduction in Km of these complexes, indicating an increased affinity for, or rate of association with, damaged naked DNA. When the damaged substrates were reconstituted into core nucleosomes (without histone H1), both normal endonuclease complexes showed a 2.5-fold enhancement of activity, which correlated kinetically with a further increase in affinity, or rate of association (decreased Km), for this damaged nucleosomal substrate. This increase in activity and in affinity was reduced but not eliminated when histone H1 was present. By contrast, neither XPA endonuclease complex showed this enhanced activity on, or affinity for, damaged core nucleosomal DNA, and actually showed decreased activity, and affinity, when histone H1 was present. Introduction, via electroporation, of either of the normal complexes into 8-MOP plus UVA treated XPA cells in culture corrected their DNA-repair defect, further confirming the role of these complexes in the repair process.     

Inactivation of aminated horseradish peroxidase by interaction with S-Sepharose

Horseradish peroxidase which had been aminated by periodate oxidation and reductive amination was purified by cation-exchange chromatography on S-Sepharose. Instead of the expected single peak of aminated enzyme, two distinct peaks of protein were eluted from the column. Evaluation of the protein in each of the two distributions showed that peak number 1 had spectral properties and specific activity similar to those of native enzyme. Distribution number 2 had a threefold reduction in the extinction in the Soret region at 404 nm and was completely devoid of enzymatic activity. This inactivation was caused by a specific interaction between the aminated peroxidase and the S-Sepharose matrix, resulting in a displacement of the heme prosthetic group out of its native orientation. The inactivation of the aminated peroxidase was found to be dependent on time, pH, and the support matrix itself. These results indicate that the S-Sepharose and Mono-S resins are not interchangeable, despite the chemical similarities of the two resins.     

Light-dependent Elongation of Anaerobically Maintained Green Pea Stem Segments and Its Implications

Anaerobic conditions reversibly inhibit the elongation of isolated green pea (Pisum sativum L. var Alaska) stem segments. Illumination of segments maintained under anoxia causes a resumption of growth. Polarographic studies show pea stem segments are photosynthetically competent as determined by O₂ evolution. Although O₂ production is totally inhibited by dichlorophenyldimethylurea (DCMU) and dinitrophenol (DNP) inhibits O₂-dependent growth, neither DCMU nor DNP completely abolishes light-dependent growth, although both reduce the effect markedly. Phenazine methosulfate promotes the growth of anaerobically maintained, illuminated, DCMU-treated segments. The data indicate that the principal effect of light in inducing growth under anaerobic conditions is the photosynthetic provision of O₂ for respiration. There is also some evidence that, at least in the absence of O₂, a small amount of elongation is due to some other light-driven process, perhaps cyclic photophosphorylation.     

Influenza Virus Reservoirs and Intermediate Hosts: Dogs,Horses, and New Possibilities for Influenza Virus Exposure of Humans

Influenza A virus (IAV) infections in hosts outside the main aquatic bird reservoirs occur periodically. Although most such cross-species transmission events result in limited onward transmission in the new host, sustained influenza outbreaks have occurred in poultry and in a number of mammalian species, including humans, pigs, horses, seals, and mink. Recently, two distinct strains of IAV have emerged in domestic dogs, with each circulating widely for several years. Here, we briefly outline what is known about the role of intermediate hosts in influenza emergence, summarize our knowledge of the new canine influenza viruses (CIVs) and how they provide key new information on the process of host adaptation, and assess the risk these viruses pose to human populations.     

Phylogenetic Framework for Trema (Celtidaceae)

We used ITS and trnL sequence data, analyzed separately and combined by MP, to explore species relationships and concepts in Trema (Celtidaceae), a pantropical genus of pioneer trees. Whether Trema is monophyletic or includes Parasponia is still unresolved. Three clades within Trema received moderate to high support, one from the New World and two from the Old World, but their relationships were not resolved. In the New World, specimens of T. micrantha formed two groups consistent with endocarp morphology. Group I, with smaller brown endocarps, is a highly supported clade sister to T. lamarckiana. Group II, with larger black endocarps, is poorly resolved with several subclades, including the highly supported T. integerrima clade. Both Old World clades contain Asian and African species, with three or more species in each region. Trema orientalis is not monophyletic: specimens from Africa formed a highly supported clade sister to T. africana, while those from Asia were sister to T. aspera from Australia.     

Non-human primate token use shows possibilities but also limitations for establishing a form of currency

Non-human primates evaluate choices based on quantitative information and subjective valuation of options. Non-human primates can learn to value tokens as placeholders for primary rewards (such as food). With those tokens established as a potential form of ‘currency’, it is then possible to examine how they respond to opportunities to earn and use tokens in ways such as accumulating tokens or exchanging tokens with each other or with human experimenters to gain primary rewards. Sometimes, individuals make efficient and beneficial choices to obtain tokens and then exchange them at the right moments to gain optimal reward. Sometimes, they even accumulate such rewards through extended delay of gratification, or through other exchange-based interactions. Thus, non-human primates are capable of associating value to arbitrary tokens that may function as currency-like stimuli, but there also are strong limitations on how non-human primates can integrate such tokens into choice situations or use such tokens to fully ‘symbolize’ economic decision-making. These limitations are important to acknowledge when considering the evolutionary emergence of currency use in our species.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.