The effect of sedimentation and microbial nitrogen regeneration in a plankton community: a simulation investigation

A computer simulation model was developed to investigate nitrogenfluxes associated with microbial interactions in plankton communities.A short time scale was used, appropriate to the build-up anddecline of phytoplankton blooms in temperate shelf waters aftera mixing or upwelling event. The model depicts a continuum ofevents, many of which have been observed in coastal, upwellingand oceanic systems, including two phytoplankton peaks correspondingto ‘new production’ and ‘regenerated production’.It predicts that nitrogen loss through sedimentation of phytoplanktonand faeces may result in a smaller bloom with a delayed onsetand prolonged duration. Microbial regeneration of nitrogen wasfound to be important in sustaining the middle stages of a phytoplanktonbloom, whereas micro- and meso-zooplankton regeneration occurredtowards the end of the bloom.     

THE EFFECTS OF SOLUBILIZATION PROCEDURES ON THE RELEASE AND MOLECULAR STATE OF ACETYLCHOLINESTERASE FROM ELECTRIC ORGAN TISSUE

Abstract— A study was made of the effect of various solubilization procedures on the release of AChE from electric organ tissue of the electric eel and on the molecular state of the enzyme. The procedures employed included homogenization in different ionic media or in the presence of detergents, etuymic treatment and chemical modification. Studies were performed on intact electroplax, tissue homogenates and membrane fractions. The apparent AChE activity of intact cells, homogenates and membrane fractions was shown to be governed by diffusion-controlled substrate and hydrogen ion gradients, generated by AChE-catalyscd hydrolysis, leading to a lower substrate concentration and a lower pH in the vicinity of the particulate enzyme.
Treatment of homogenates with NaCl solutions or with NaCl solutions containing the nonionic detergent Triton X-100 causes release of the native'molecular forms of the enzyme (primarily the 18 S species) which aggregate at low ionic strength. For optimal extraction both high ionic strength (e.g. 1 M-NaCl) and the detergent are needed AChE is also solubilized by treatment of tissue homogenates with trypsin, bacterial protease or collagenase. The first two enzymes caused its release as an 11 S non-aggregating form, while collagenase also produces a minor non-aggregating - 16 S component. Treatment of tissue homogenates with maleic anhydride causes release of AChE as a non-aggregating 18 S species. On the basis of the solubilization experiments it is concluded that the interaction of AChE with the excitable membrane is primarily electrostatic. The possible orientation of the enzyme within the synaptic gap is discussed.     

Assessment of uncoupling activity of uncoupling protein 3 using a yeast heterologous expression system.

Uncoupling protein 3L, uncoupling protein 1 and the mitochondrial oxoglutarate carrier were expressed in Saccharomyces cerevisae. Effects on different parameters related to the energy expenditure were studied. Both uncoupling protein 3L and uncoupling protein 1 reduced the growth rate by 49% and 32% and increased the whole yeast O2 consumption by 31% and 19%, respectively. In isolated mitochondria, uncoupling protein 1 increased the state 4 respiration by 1.8-fold, while uncoupling protein 3L increased the state 4 respiration by 1.2-fold. Interestingly, mutant uncoupling protein 1 carrying the H145Q and H147N mutations, previously shown to markedly decrease the H+ transport activity of uncoupling protein 1 when assessed using a proteoliposome system (Bienengraeber et al. (1998) Biochem. 37, 3-8), uncoupled the mitochondrial respiration to almost the same degree as wild-type uncoupling protein 1. Thus, absence of this histidine pair in uncoupling protein 2 and uncoupling protein 3 does not by itself rule out the possibility that these carriers have an uncoupling function. The oxoglutarate carrier had no effect on any of the studied parameters. In summary, a discordance exists between the magnitude of effects of uncoupling protein 3L and uncoupling protein 1 in whole yeast versus isolated mitochondria, with uncoupling protein 3L having greater effects in whole yeast and a smaller effect on the state 4 respiration in isolated mitochondria. These findings suggest that uncoupling protein 3L, like uncoupling protein 1, has an uncoupling activity. However, the mechanism of action and/or regulation of the activity of uncoupling protein 3L is likely to be different.     

Molecular cloning of rabbit CARP cDNA and its regulated expression in adriamycin-cardiomyopathy.

A full-length rabbit cDNA of cardiac adriamycin responsive protein (CARP) has been cloned. It shows high levels of identity at the amino acid sequence level (>86%) with the rat, mouse and human homologues. CARP mRNA levels are highly regulated in adriamycin-cardiomyopathy in rabbits.     

Correlation between the bone mass of athletes and biochemical and genetic markers of bone tissue remodeling

The association of the polymorphism of the VDR, Col1a1, and CALCR genes with a form of osteoporosis frequently occurring as a consequence of intense physical exercise in athletes was studied. Biochemical parameters of bone remodeling and its neuroendocrine regulation, as well as the bone masses, of 22 amateur athletes were determined immediately before a strenuous nine-week training cycle (TC) and eight months later. The possible association of these factors with the polymorphism of the genes coding for bone tissue proteins was studied. Long-term intense physical training was found to be associated with a significant activation of bone tissue resorption accompanied by continued rapid synthesis. Nevertheless, and in spite of the strong activation of resorption caused by the TC, the athletes exhibited no osteoporosis (even eight months after the discontinuation of the TC); some of them, however, displayed an individual tendency to osteopenia. According to the results of genetic analysis, this was associated with the polymorphism of predisposition genes (genotype TT of the VDR gene and the functionally weakened s allele of the Col1a1 gene).     

Direct Comparisons of 2D and 3D Dental Microwear Proxies in Extant Herbivorous and Carnivorous Mammals

The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately.     

Radioimmunoassay for beta-endorphin (1-18), a novel pituitary peptide derived from proopiomelanocortin

A specific radioimmunoassay was developed for beta-endorphin (1-18). The content of beta-endorphin (1-18) immunoreactivity in rat tissues was as follows: posterior pituitary 260 ng/fragment, anterior pituitary 1.46 ng/mg, hypothalamus 11.9 pg/mg. The levels were undetectable (less than 3 pg/mg) in extrahypothalamic brain, pancreas, small intestine, prostata and testis. Gel filtration and reverse-phase HPLC studies indicated that most of rat anterior pituitary immunoreactivity is due to native beta-endorphin (1-18), whereas the bulk of posterior pituitary immunoreactivity corresponds to more hydrophobic material, probably N-acetyl-beta-endorphin (1-18). Thus, beta-endorphin (1-18) is a quantitatively important novel pituitary peptide derived from proopiomelanocortin. The posterior pituitary is an especially rich source of (N-acetyl)-beta-endorphin (1-18).     

Reversible hyperphosphorylation and reorganization of vimentin intermediate filaments by okadaic acid in 9L rat brain tumor cells.

Okadaic acid (OA), a protein phosphatase inhibitor, was found to induce hyperphosphorylation and reorganization of vimentin intermediate filaments in 9L rat brain tumor cells. The process was dose dependent. Vimentin phosphorylation was initially enhanced by 400 nM OA in 30 min and reached maximal level (about 26-fold) when cells were treated with 400 nM OA for 90 min. Upon removal of OA, dephosphorylation of the hyperphosphorylated vimentin was observed and the levels of phosphorylation returned to that of the controls after the cells recovered under normal growing conditions for 11 h. The phosphorylation and dephosphorylation of vimentin induced by OA concomitantly resulted in reversible reorganization of vimentin filaments and alteration of cell morphology. Cells rounded up as they were entering mitosis in the presence of OA and returned to normal appearance after 11 h of recovery. Immuno-staining with anti-vimentin antibody revealed that vimentin filaments were disassembled and clustered around the nucleus when the cells were treated with OA but subsequently returned to the filamentous states when OA was removed. Two-dimensional electrophoresis analysis further revealed that hyperphosphorylation of vimentin generated at least seven isoforms having different isoelectric points. Furthermore, the enhanced vimentin phosphorylation was accompanied by changes in the detergent-solubility of the protein. In untreated cells, the detergent-soluble and -insoluble vimentins were of equal amounts but the solubility could be increased when vimentins were hyperphosphorylated in the presence of OA. Taken together, the results indicated that OA could be involved in reversible hyperphosphorylation and reorganization of vimentin intermediate filaments, which may play an important role in the structure-function regulation of cytoskeleton in the cell.