The determination of the kinetics of polysaccharide thermal degradation using high temperature viscosity measurements

Information about the thermal degradation of the polysaccharides sodium alginate, carrageenan and carboxymethyl cellulose has been obtained from the time dependence of the viscosity at high temperatures measured using a slit viscometer. The viscosity is related to the molecular weight using previously-published relations between the zero shear specific viscosity and the coil overlap parameter in conjunction with the appropriate Mark-Houwink equation. It is found that alginate is much less stable than carboxymethyl cellulose and carrageenan. Activation energies for depolymerisation obtained from Arrhenius plots in the presence of oxygen ranged from 50 kJ/mol for alginate to 105 kJ/mol for κ-carrageenan.     

Nematode Mitochondrial DNA: Anomalies and Applications

The mitochondrial genome of animal cells is currently under intense investigation by molecular, evolutionary, and population biologists. This review summarizes the available information on the molecular biology of nematode mitochondrial DNA and explains how the fundamental knowledge obtained from these basic studies may be applied to nematode systematics, evolution, and diagnostics.     

Singlet oxygen: a potential culprit in myocardial injury?

The purpose of this study was to explore the role of singlet oxygen in cardiovascular injury. To accomplish this objective, we investigated the effect of singlet oxygen [generated from photoactivation of rose-bengal] on the calcium transport and Ca²⁺-ATPase activity of cardiac sarcoplasmic reticulum and compared these results with those obtained by superoxide radical, hydrogen peroxide and hydroxyl radical. Isolated cardiac SR exposed to rose bengal (10 nM) irradiated at (560 nm) produced a significant inhibition of Ca ²⁺ uptake; from 2.27 ± 0.05 to 0.62 ± 0.05 µmol Ca⁺/mg.min (mean ± SE) (P < 0.01) and Ca²⁺-ATPase activity from 2.08 ± 0.05 µmol Pi/min. mg to 0.28 ± 0.04 µmol Pi/min. mg (mean ± SE) (P < 0.01). The inhibition of calcium uptake and Ca²⁺-ATPase activity by rose bengal derived activatedoxygen (singlet oxygen) was dependent on the duration of exposure and intensity of light. The singlet oxygen scavengers ascorbic acid and histidine significantly protected SR Ca²⁺-ATPase against rose bengal derived activated oxygen species but superoxide dismutase and catalase did not attenuate the inhibition. SDS-polyacrylamide gel electrophoresis of SR exposed to photoactivated rose bengal up to 14 min, demonstrated complete loss of Ca²⁺-ATPase monomer band which was significantly protected by histidine. Irradiation of rose bengal also caused an 18% loss of total sulfhydryl groups of SR. On the other hand, superoxide (generated from xanthine oxidase action on xanthine) and hydroxyl radical (0.5 mM H₂O₂ + Fe²⁺ -EDTA) as well as H₂O₂ (12 mM) were without any effect on the 97,000 dalton Ca²⁺-ATPase band ofsarcoplasmic reticulum. The results suggest that oxidative damage of cardiac sarcoplasmic reticulum may be mediated by singlet oxygen. This may represent an important mechanism by which the oxidative injury to the myocardium induces both a loss of tension development and arrhythmogenesis.     

Monoclonal antibody-based immunoassay of vitellogenin in the blood of male channel catfish (Ictalurus punctatus).

1. A monoclonal antibody to vitellogenin of channel catfish (Ictalurus punctatus) was made, and its specificity was demonstrated using Western blots of serum from female fish, estradiol-treated male fish, untreated male fish, vitellogenin purified by three different methods and egg extracts. 2. An enzyme-linked immunosorbent assay (ELISA), using this monoclonal antibody, detected vitellogenin in the plasma of 59 out of 60 untreated 17-24-month-old male channel catfish with a mean concentration of 338 micrograms/ml and a maximum concentration of 4240 micrograms/ml. 3. Vitellogenin levels in male channel catfish were unrelated to testicular stage, gonadosomatic index and month.     

The influence of salinity on the kinetics of NH inf4 sup+ uptake in Spartina alterniflora

Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH _inf4 ^sup+ uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent K_m but did not significantly affect V_max (mean V_max=4.23±1.97 mole·g^–1·h^–1). The apparent K_m increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH _inf4 ^sup+ uptake in S. alterniflora. No significant NH _inf4 ^sup+ uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both V_max and K_m. Reduction of solution salinity from 35 to 5 g/L did not change V_max but reduced K_m by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in V_max of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH _inf4 ^sup+ . For both experiments, increasing salinity led to an increase in the apparent K_m similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH _inf4 ^sup+ uptake kinetics.     

Energy allocation in the cladoceran Daphnia magna Straus,under starvation and refeeding

Summary Models incorporating the energetics of individual daphnids (Cladocera) have been developed to predict the effect of environmental variables, particularly food availability, on population dynamics. One of them, that of Kooijman (1986), assumes that all assimilated energy enters a storage compartment prior to use in production and metabolism, and that under starvation the stores are used to support maintenance, reproduction and somatic growth, in that order of priority. This predicts that, under starvation, reproduction and growth will continue for a time, and that after they cease death will be immediate. Another model, that of McCauley et al. (1990), assumes that assimilated energy is used directly for maintenance and production, and that stores are accumulated to support maintenance metabolism under starvation. This predicts that growth and reproduction should cease immediately upon starvation and that death will not be immediate. We have carried out laboratory experiments, manipulating starvation time, on Daphnia magna to distinguish between these two models. The results support features of both models in that reproduction, but not growth, ceases upon starvation. We therefore developed a third model in which both maintenance and growth are supported from stores under starvation, with maintenance taking priority over growth under these conditions.     

Investigation of the neutral filter elution technique I. Effects of pore density and pore diameter on elution rate at pH 9.6

To understand better the biophysical mechanism of neutral filter elution (pH 9.6), we eluted genomes of known size and shape: coliphage T4c (Mr 1.15 x 10(8), E. coli (Mr 2.7 x 10(9)), and Chinese hamster lung fibroblasts (V79, Mr 2-4 x 10(10)). DNA eluted through 15% sucrose atop the filter in a biphasic pattern. The elution rate of the initial component correlated (r greater than 0.97) exponentially with 1/Mr for monodisperse samples of DNA eluted through pore sizes 0.1-3.0 microns. Using this relationship between elution rate and Mr, we estimated Mn of polydisperse, X-irradiated (253 Gy) samples of DNA from E. coli or V79 cells to be 3.15 +/- 1.46 and 1.42 +/- 0.33, respectively, compared to expected values of 2.93 and 3.52 (10(8) Da). The best predictor of elution rate for DNA from T4c and intact and X-irradiated V79 cells was pore density, and pore diameter for DNA from X-irradiated E. coli. The rate of elution of DNA from unirradiated E. coli was unrelated to pore density or diameter. While the mechanism of neutral filter elution remains unknown, its use for linear DNAs with Mn ca. 10(8) Da appears to be valid quantitatively.