Kinetic studies of the oxidation of glutathione in protein refolding buffer

Here, we examined the change of glutathione (GSH) under different conditions and determined the appropriate kinetic schemes to describe its change of concentration. GSH was continuously oxidized into glutathione disulfide (GSSG) as incubation period increased at the temperatures ranging from 10 to 50 °C while certain oxidation by-products were also observed at the later stage of reaction at higher temperatures (70–90 °C). The addition of 0.3 mM GSSG in 3 mM GSH solution delayed the onset of GSH oxidation without significantly changing the rate of GSH oxidation. Our results also revealed that GSH oxidation could be facilitated upon the addition of copper (II) ion whereas GSH oxidation was found to be decelerated when EDTA was present. In kinetic analysis, the reaction orders of GSH oxidation under various conditions were determined. Moreover, the temperature dependence of the rate of GSH oxidation was modeled by Arrhenius and Eyring equations and resultant activation parameters were also presented.     

A Comparison of Generalized Poisson Distribution for Modeling Chromosome Aberrations

Various models have been developed for modeling the distribution of chromosome aberrations in the literature (e. g. Consul, 1989). Generalized Poisson distribution is among the popular ones. The parameters of this distribution provide meaningful interpretation of the induction mechanism of the chromosome aberrations. In this article, we apply several estimation methods to estimate the generalized Poisson parameters for fitting the number of chromosome aberrations under different dosages of radiations. The methods compared are moment, maximum likelihood, minimum chi-square, weighted discrepancy and empirically weighted rates of change. Our study suggests that the empirically weighted rates of change method results in smallest Mean Square Error and Mean Absolute Error for most dosages of radiations. The data used for this comparison are from Janardan and Schaeffer (1977).     

Regulation of hydrogen metabolism in Butyribacterium methylotrophicum by substrate and pH

 Exogenous H₂/CO₂ and glucose were consumed simultaneously by Butyribacterium methylotrophicum when grown under glucose-limited conditions. CO₂ reduction to acetate was coupled to H₂ consumption. The addition of either H₂ or CO₂ to glucose batch fermentation resulted in an increase in cell density, hydrogenase (H₂-consuming and -producing) activities and fatty acid production by B. methylotrophicum as compared to when N₂ was the feed gas. Hydrogenase activities appeared to be tightly regulated and were produced at higher rates during the exponential phase when CO₂ was the feed gas as compared to H₂ or N₂. The increase in H₂-consuming activity and decrease in H₂-producing activity was correlated with an increase in butyrate synthesis. H₂-consuming and ferredoxin (Fd)–NAD reductase activities increased while H₂-producing and NADH–Fd reductase activities decreased in cells grown at pH 5.5 compared to those at pH 7.0. The molar ratio of butyrate/acetate was shifted from 0.35 at pH 7.0 to 1.22 at pH 5.5. The addition of exogenous H₂ did not decrease the butyrate/acetate ratio at pH 7.0 nor at pH 5.5. The results indicated that growth pH values regulated both hydrogenase and Fd–NAD oxidoreductase activities such that, at acid pH, more intermediary electron flow was directed towards butyrate synthesis than H₂ production. Received: 22 August 1995/Received revision: 18 December 1995/Accepted: 22 January 1996     

Photoprotective mechanisms in cold-acclimated and nonacclimated needles of <Emphasis Type="Italic">Picea glehnii</Emphasis>

The response of Picea glehnii, a cold-tolerant species in the boreal zone, to air temperature (T) was investigated for its cold-acclimated needles (i.e. the ones subjected to gradual decrease in T) and nonacclimated needles (i.e. the ones subjected to a sudden decrease in T) were compared under low temperature. Cold-acclimated needles showed a greater increase of zeaxanthin and lutein contents than nonacclimated ones, whereas the nonacclimated needles showed a greater increase of thylakoid-bound ascorbate peroxidase (tAPX) activity than cold-acclimated ones under chilling conditions (after cold acclimation). These results suggest that: (1) low T induces the increase of zeaxanthin and lutein content, and tAPX activity; (2) accumulated zeaxanthin and lutein protect needles from photooxidative stress by dissipating excess energy before the reactive oxygen species (ROS) are formed in response to a gradual decrease in T (with cold acclimation and subsequent chilling condition), and by tAPX scavenging ROS formed in the case of a sudden decrease in T (without cold acclimation and chilling condition).     

Copepod grazing in turbulent flow: elevated foraging behavior and habituation of escape responses

When exposed to non-turbulent followed by turbulent conditions,the copepod Centropages hamatus initially responded with numerousescape reactions and increased foraging behavior. However, whenthe cycle of non-turbulent followed by turbulent flow was repeatedfor several consecutive cycles, the two behaviors followed distinctlydifferent patterns. Foraging effort increased during the firsttwo cycles, and then remained at high levels during both turbulentand non-turbulent periods (period durations of 12.5 and 25 min).In contrast, escape behavior habituated rapidly during eachturbulent period and dishabituated during each non-turbulentperiod. These response patterns are suited to the strongly intermittentnature of oceanic turbulence and allow C.hamatus to utilizethe benefits of enhanced encounter rate, while minimizing theexpense of unnecessary escape responses.     

Phylogenetic inferences introduced on cytochrome b gene sequences data for six flatfish species (Teleostei, Pleuronectidae) and species synonymy between representatives of genera Pseudopleuronectes and Hippoglossoides from far eastern seas

Cytochrome b (Cyt-b) gene was sequenced for six flatfish species and compared with seven other species belonging to Pleuronectiformes. Monophyly of the family Pleuronectidae representatives was fine supported by bootstrap or other means in several sequence-based trees on Cyt-b gene data. Results revealed that synonymy must be accepted for Hippoglossoides elassodon, and H. robustus, as well as for Pseudopleuronectes yokohamae, and P. schrenki. This article was submitted by the authors in English.     

The effects of the metal ions Mn2+ and Co2+ on muscle contraction in the Norway lobster Nephrops norvegicus (L.)

The effects of the metal ions manganese and cobalt on force production by the abdominal superficial flexor muscle of the Norway lobster, Nephrops norvegicus, have been studied in response to both neuronal stimulation and electrical field stimulation applied to an isolated neuromuscular preparation, and by selectively blocking synaptic transmission with ivermectin. In response to both forms of stimulation, low concentrations of manganese added to the standard N. norvegicus saline increased the contractile force produced by the muscle, whereas higher concentrations of manganese inhibited both responses in a dose-dependent manner, until force was completely abolished at concentrations above 2.9 mM manganese. Cobalt ions produced similar effects, and no significant difference was found between the concentration of the two ions at 50% force inhibition (K_m) or between the two stimulation methods (manganese: 1.22 mM; cobalt: 1.29 mM, P = 0.86). This suggests that they have a similar mode of action, and a postsynaptic site of inhibition. These K_m values are considerably higher than the concentrations of these ions known to accumulate in the haemolymph of N. norvegicus under eutrophic conditions, and it therefore seems unlikely that accumulations of manganese or cobalt ions under such conditions would cause any significant inhibition of muscle contraction force. Accepted: 28 April 1999     

Glyceraldehyde-3-phosphate dehydrogenase as a biochemical marker of cytotoxicity by vinyl sulfones in cultured murine spleen lymphocytes

Recently, vinyl sulfones have been observed to selectively inhibit glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is an important ATP-generating enzyme in glycolysis. The possibility of using GAPDH as a biochemical parameter of cytotoxicity by vinyl sulfones was investigated using mouse lymphocytes. Incubation of lymphocyte GAPDH with ethylvinyl sulfone resulted in a pseudo-first-order loss of enzyme activity. The exposure of lymphocytes to ethylvinyl sulfone resulted in the decrease of GAPDH activity followed by ATP depletion and cell death, which were both dependent on the concentration of ethylvinyl sulfone. A further study on the time-dependent change indicated that cell death was preceded by ATP loss. Compared to ethylvinyl sulfone, divinyl sulfone was more than 8 times more potent in causing either ATP depletion or cell death.Abbreviations DTT dithiothreitol - GAPDH glyceraldehyde-3-phosphate dehydrogenase - NAD nicotinamide adenine dinucleotide     

Changes in the Non-Photochemical Quenching of Chlorophyll Fluorescence During Aging of Wheat Flag Leaves

Non-photochemical quenching of chlorophyll fluorescence (q_N) and its three components (q_Nf, q_Nm, and q_Ns) in the flag leaves of wheat grown in the field were studied by a fluorometer PAM-2000 on clear days. The diurnal variation patterns of q_N in just fully extended (JFEL) and aging leaves (AL) were similar, but q_Nm declined markedly in JFEL while it remained at a relatively high level in AL under strong sunlight at noon. Furthermore, at midday q_Nf was higher than q_Ns in JFEL, but much lower in AL. The results show the relative contributions of different mechanisms in preventing the photosynthetic apparatus from photodamage change during leaf development. This revised version was published online in June 2006 with corrections to the Cover Date.