The effect of copper on glutathione metabolism in human leukocytes

Leukocytes incubated with Cu(II) showed a decrease in both glutathione reductase activity and reduced glutathione content. The glucose 6-phosphate dehydrogenase activity under the same conditions was not affected. Serum albumin added to mixtures prevented the loss of enzyme activity, whiled-penicillamine andl-histidine had little effect. Prior oxidation of the cell-reduced glutathione did not diminish the enzyme inhibitory action of Cu(II). The amount of regeneration of reduced glutathione in leukocytes previously treated with diamide to oxidize their reduced glutathione was a function of Cu(II) concentration in the media. No evidence was obtained that elevated serum ceruloplasmin levels in rabbits, nor incubation of leukocytes in vitro with ceruloplasmin, affect leukocyte glutathione reductase activity. It was proposed that the major mechanism by which copper affects glutathione metabolism in leukocytes is by inhibition of glutathione reductase.     

The antimutagenic effect of selenium on 7,12-dimethylbenz(a)anthracene and metabolites in the amesSalmonella/microsome system

The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene, and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na₂SeO₃ reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion. Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na₂SeO₄ inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that form and concentration are important factors in this trace element's efficacy.     

Differentiation between the somatostatin inhibition and the post-somatostatin rebound observed on growth hormone secretion in vitro

A rebound in growth hormone secretion following somatostatin treatment has been shown in several systems where somatostatin suppresses secretion of the hormone. We have developed an in vitro system in which isolated and cultured pituitary cells were perfused after mild trypsinization. After washing, these cells retained their sensitivity and secreted growth hormone (GH) in response to physiological activators (norepinephrine, dopamine, serotonin) or inhibitors (somatostatin) as well as pharmacological activators (PGE2). The variation in GH secretion occurred within a minute after commencement of the infusion and was as rapidly reversible and repeatable minutes later. During somatostatin infusion the GH secretion was not totally suppressed (residual secretion (mean +/- S.D.) 34 +/- 7%). After the infusion a rapid rebound in GH secretion occurred, reaching levels in excess of the pretreatment value of 138 +/- 13%. This rebound effect occurred at doses higher than (10(-10)M) but not at lower doses, even when significant inhibition was observed. The inhibitory effect is of greater magnitude than the rebound effect (rebound = inhibition X 57 +/- 7% (mean +/- S.D.)). Furthermore, rebound was not enhanced by prolongation of somatostatin infusion. These latter results indicate that the rebound in secretion cannot be explained on the sole basis of storage of intracellular GH during somatostatin infusion and in fact suggest the involvement of a process of GH degradation and/or an inhibition of GH synthesis.     

Regulation of cellular energy metabolism. The Crabtree effect

The Crabtree effect (inhibition of respiration by glycolysis) is observed in cells with approximately equal glycolytic and respiratory capacities for ATP synthesis. Addition of glucose to aerobic suspensions of glucose-starved cells (Sarcoma 180 ascites tumor cells) causes a burst of respiration and lactate production due to ATP utilization for glucose phosphorylation by hexokinase and phosphofructokinase. This burst of activity is followed by inhibition of both respiration and glycolysis, the former to below the value before glucose addition (Crabtree effect). Both the respiratory rate and the glycolytic flux appear to be regulated by the cytosolic $\text{[}\text{ATP}\text{]}\text{[}\text{ADP}\text{][}\text{P}{}_{\mathrm{i}}\text{]}$ albeit by completely different mechanisms. Respiration is regulated by the free energy of hydrolysis of ATP, such that the rate increases as the $\text{[}\text{ATP}\text{]}\text{[}\text{ADP}\text{][}\text{P}{}_{\mathrm{i}}\text{]}$ decreases and decreases as the $\text{[}\text{ATP}\text{]}\text{[}\text{ADP}\text{][}\text{P}{}_{\mathrm{i}}\text{]}$ increases. The regulatory enzymes of glycolysis are activated by ADP (AMP) and P_i and inhibited by ATP. Thus both respiration and glycolysis increase or decrease as the $\text{[}\text{ATP}\text{]}\text{[}\text{ADP}\text{][}\text{P}{}_{\mathrm{i}}\text{]}$ decreases or increases. The parallel regulation of both ATP-producing pathways by this common metabolite ratio is consistent with the cytoplasmic $\text{[}\text{ATP}\text{]}\text{[}\text{ADP}\text{][}\text{P}{}_{\mathrm{i}}\text{]}$ being an important determinant of homeostatic regulation of cellular energy metabolism.     

Regulation of excitation energy distribution in Photosystem-II fragments by magnesium ions

Fluorescence characteristics of Photosystem-II subchloroplasts (TSF-II and TSF-IIa) fractionated by Triton X-100 treatment were studied in relation to cation-induced regulation of excitation-energy distribution within subchloroplast fragments. Absorption spectra and fluorescence-emission spectra at 77 K showed that TSF-II contains the light-harvesting chlorophyll-protein complex in addition to the reaction-center complex, which is present alone in TSF-IIa.Mg²⁺ increased the ratio of F_695nm to F_685nm in the fluorescence-emission spectrum of TSF-II particles at 77 K, but had no effect on TSF-IIa particles. Mg²⁺ also induced a quenching of chlorophyll fluorescence at room temperature in TSF-II, an effect that was insensitive to the presence of DCMU. The DCMU-insensitive fluorescence quenching was not observed in the TSF-IIa preparation. These results suggest an existence of cation-induced regulation of excitation-energy transfer in TSF-II preparations. Presence of antenna chlorophyll molecules alone does not seem to be sufficient for observing energytransfer regulation by cations in Photosystem-II preparations.     

Change in apparent and true absorption and retention of dietary zinc with age in rats

Two groups of 16 rats each were fed the same diet with 12.9 ppm Zn. Nine days after each animal was injected with⁶⁵Zn for assessing fecal zinc of endogenous origin, zinc intake and excretion were determined for a six-day period at the age of about five (group I) and nine (II) weeks. At mean growth rates of 5.1 and 5.2 g/day, food consumption per gram of gain was 2.01 g in group I vs 2.86 g in II. Overall, zinc retention amounted to 21 vs 25 μg Zn/g of gain. Apparent absorption averaged 92 vs 74% of Zn intake (132 vs 189 μg/day), while true absorption averaged 98 vs 92%. It was concluded that endogenous fecal zinc excretion was limited to the indispensable loss (F _em) in group I (7 μg/day), while it exceeded this minimum loss in group II (33 μg/day). True retention, which reflected total zinc utilization (true absorption times metabolic efficiency), was derived from apparent absorption plusF _em (11 μg/day for group II according to the greater metabolic body size of the rats). It averaged 98% of Zn intake in group I vs 80% in group II. The mean metabolic efficiency was 100% vs 87%. The conclusion was that these marked differences between age groups in utilizing the dietary zinc reflected the efficient homeostatic adjustments in absorption and endogenous excretion of zinc to the respective zinc supply status.     

Effect of inhibitors and uncouplers on light-induced potential changes triggering photophobic responses

Light-energy absorption by Microcystis aeruginosa with and without gas vacuoles was observed, respectively by using an integrating sphere photometer. As far as the concentration of cell suspension of the order of 10⁶⁷ cells/ml in this work was concerned, the performance of gas vacuoles to shield incident light was most unlikely. Referring to a correlation secured by the integrating sphere photometer between light absorption and cell concentration of the suspension, a turbidostat culture of the blue-green alga demonstrated that the growth efficiency, Y _kJ defined as g cells harvested per kJ of light energy absorbed by the cells was nearly 0.004. This value of Y _kJ was almost the same as that of Spirulina platensis.Abbreviation vvm volume of air per volume of medium per min     

Observations on the in vitro culture of Cotylurus erraticus (Trematoda: Strigeidae)

Mtitchell J. S., Halton D. W. and Smyth J. D. 1978. Observations on the in vitro culture of Cotylurus erraticus (Trematoda: Strigeidae). International Journal for Parasitology8: 389–397. Cotylurus erraticus metacercariae obtained from around the heart of rainbow trout were excysted and grown in vitro and in vivo to egg-producing adults. For in vitro development, tissue culture media M199 or NCTC 135 was used, together with varying amounts of chicken serum. Worms grown in media containing the highest concentration of serum (80% per volume) showed the fastest rate of development, measured by the time taken for the first eggs to appear in the uterus. The testes, ovaries and vitellaria of these worms were comparable in structure and histochemistry with those of worms reared in gulls. Eggs were produced by worms in all media containing chicken serum, but the eggs had abnormal shells and failed to embryonate.