Effect of intermittent CO2 enrichment during nutrient starvation on tertiary treatment of wastewater by alginate-immobilized Scenedesmus bicellularis

A method of accelerating the removal of ammonium and phosphate by the unicellular microalga Scenedesmus bicellularis is presented for municipal tertiary wastewater treatment using immobilized cells to obtain a high quality of effluents. Microalgal cells grown in defined medium were harvested by centrifugation and stored at 4°C in the dark for 8 months before immobilization. The concentrated cell suspension was then immobilized in alginate films supported on polypropylene screens. Immobilized cells were incubated in a water-saturated air stream enriched with CO₂ at 750, 1,000, or 1,500 ppm for 3 h periods followed by 2 h periods without enrichment. The quantitative effects of these three CO₂ enrichments on nutrient uptake from secondary municipal wastewater effluent were compared to a control laboratory air at 320 ppm under the same conditions of illumination, photoperiod, and humidity. The exposure cycle of 48-h nutrient deprivation in air with CO₂ enrichment followed by 2 h of nutrient uptake from wastewater was repeated three times with a residual NH₄---N content dropping to 0% after 105 min for the 1,500 ppm CO₂ treatment and to 34% of the initial level after 120 min for the control treatment. Complete PO₄---P removal required more than 2 h. The chlorophyll a contents obtained with 1,000 and 1,500 ppm CO₂ enrichments were comparable. This study establishes that intermittent CO₂ enrichment during nutrient deprivation of immobilized microalgal cells in a water-saturated air stream may accelerate tertiary wastewater treatment.     

Importance of mitochondrial transmembrane processes in human mitochondriopathies

In a substantial group of subjects suspected to have a mitochondriopathy no defect in the mitochondrial energy metabolism (pyruvate dehydrogenase complex or respiratory chain complexes) can be demonstrated. At least in some of these subjects it seems justified to consider a defect in one of the proteins which mediate the transport of several ions and substrates across the mitochondrial membranes. Of particular interest are proteins which are directly involved in the process of oxidative phosphorylation, such as the adenine nucleotide translocator (ANT) and the phosphate carrier (PiC). However, defects in transmembrane ion transporters also may induce impaired energy metabolism probably as a result of osmotic disturbances within the mitochondrial matrix. In this respect, the voltage-dependent anion channel (VDAC) and other ion channels have to be taken into consideration. Here we review the still incomplete knowledge of the occurrence of ANT, PiC, VDAC, cation channels, and a few substrate carriers in human tissues, as well as their possible role in pathology.     

The Effect of Chronic Treatment with the GABA Transaminase Inhibitors γ-Vinyl-GABA and Ethanolamine-O-Sulphate on the In Vivo Release of GABA from Rat Hippocampus

Abstract: The effects of chronic treatment with the specific, mechanism-based, irreversible inhibitors of 4-aminobutyrate aminotransferase (EC 2.6.1.19; GABA transaminase), ethanolamine O -sulphate (EOS), and 4-aminohexenoate [vigabatrin; γ-vinyl-GABA (GVG)] on the extracellular concentrations of GABA in the hippocampus have been studied using in vivo microdialysis in conscious animals. Oral dosing [3 mg/ml of drinking water, giving doses of GVG of 194 ± 38 mg/kg/day and of EOS of 303 ± 42 mg/kg/day (mean ± SD)] was followed by microdialysis at 2, 8, and 21 days. The basal outflow of GABA (in the range of ∼1–2 pmol/30 µl/30-min sample) after 2 and 8 days of treatment was not significantly different from that in control animals, but the 21-day treatment gave significant rises in the extracellular GABA concentration (up to ∼6–8 pmol/30 µl/30-min sample). Both inhibitors gave similar results. Depolarisation with 100 m M K⁺ gave large increases in GABA release in control (∼20–60 pmol/30 µl/30-min sample) and treated animals. The 8- and 21-day-treated animals showed significant increases in the stimulated release compared with control animals (∼80–100 pmol/30 µl/30-min sample). Excluding Ca²⁺ had no significant effect on either basal or stimulated release. The significant increases in K⁺-evoked release of GABA show that the increased intracellular pool of GABA is available for release, and this may be related to the anticonvulsant action of these compounds.     

Active site model for gamma-aminobutyrate aminotransferase explains substrate specificity and inhibitor reactivities.

A homology model for the pig isozyme of the pyridoxal phosphate-dependent enzyme gamma-aminobutyrate (GABA) aminotransferase has been built based mainly on the structure of dialkylglycine decarboxylase and on a multiple sequence alignment of 28 evolutionarily related enzymes. The proposed active site structure is presented and analyzed. Hypothetical structures for external aldimine intermediates explain several characteristics of the enzyme. In the GABA external aldimine model, the pro-S proton at C4 of GABA, which abstracted in the 1,3-azaallylic rearrangement interconverting the aldimine and ketimine intermediates, is oriented perpendicular to the plane of the pyridoxal phosphate ring. Lys 329 is in close proximity and is probably the general base catalyst for the proton transfer reaction. The carboxylate group of GABA interacts with Arg 192 and Lys 203, which determine the specificity of the enzyme for monocarboxylic omega-amino acids such as GABA. In the proposed structure for the L-glutamate external aldimine, the alpha-carboxylate interacts with Arg 445. Glu 265 is proposed to interact with this same arginine in the GABA external aldimine, enabling the enzyme to act on omega-amino acids in one half-reaction and on alpha-amino acids in the other. The reactivities of inhibitors are well explained by the proposed active site structure. The R and S isomers of beta-substituted phenyl and p-chlorophenyl GABA would bind in very different modes due to differential steric interactions, with the reactive S isomer leaving the orientation of the GABA moiety relatively unperturbed compared to that of the natural substrate. In our model, only the reactive S isomer of the mechanism-based inhibitor vinyl-GABA, an effective anti-epileptic drug known clinically as Vigabatrin, would orient the scissile C4-H bond perpendicular to the coenzyme ring plane and present the proton to Lys 329, the proposed general base catalyst of the reaction. The R isomer would direct the vinyl group toward Lys 329 and the C4-H bond toward Arg 445. The active site model presented provides a basis for site-directed mutagenesis and drug design experiments.     

The mobile ferrous iron pool in Escherichia coli is bound to a phosphorylated sugar derivative

Based on in vivo Mössbauer spectroscopy it has previously been demonstrated that the intracellular iron pool of Escherichia coli, grown in iron deficient media supplemented with siderophores as the sole iron source, is dominated by a single Fe²⁺ and a single Fe³⁺ species. We have isolated the ferrous ion species and have purified it employing native column PAGE, chromatography and ultrafiltration. The purified compound displays an M _app of 2.2 kDa and an extremely low isoelectric point (pI) of 1.05. It is shown that this ferrous ion binding compound is neither a protein nor a nucleotide, rather it is composed mainly of phosphorylated sugar derivatives. This compound binds approximately 40% of the cytoplasmic iron. Therefore it is proposed that this oligomeric ferrous carbohydrate phosphate represents the long sought after mobile, low molecular mass iron pool.     

A model of the pentose phosphate pathway in rat liver cells

A mathematical model based on kinetic data taken from the literature is presented for the pentose phosphate pathway in fasted rat liver steady-state. Since the oxidative and non oxidative pentose phosphate pathway can act independently, the complete (oxidative + non oxidative) and the non oxidative pentose pathway were simulated.Sensitivity analyses are reported which show that the fluxes are mainly regulated by D-glucose-6-phosphate dehydrogenase (for the oxidative pathway) and by transketolase (for the non oxidative pathway). The most influent metabolites were the group ATP, ADP, P₁ and the group NADPH, NADP⁺ (for the non oxidative pathway).Abbreviations GK Glucokinase, (E.C. 2.7.1.2.) - G6PDH D-glucose-6-phosphate dehydrogenase, (E.C. 1.1.1.49) - PLase 6-Phosphogluconelactonase, (E.C. 3.1.1.31.) - PGIcDH 6-Phosphogluconate dehydrogenase, (E.C. 1.1.1.44) - RPI D-ribose-5-phosphate keto-isomerase, (E.C. 5.3.1.6) - TK D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycol-aldehyde transferase, (E.C. 2.2.1.1.) - TA D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate dihydroxyacetone transferase, (E.C. 2.2.1.2) - EP D-ribulose-5-phosphate-3-epimerase, (E.C. 5.1.3.1) - PGI D-glucose-6-phosphate keto-isomerase, (E.C. 5.3.1.9) - TPI D-glyceraldehyde-3-phosphate keto-isomerase, (E.C.5.3.1.1)     

Response of the rat heart to catecholamines and thyroid hormones

Catecholamines and thyroid hormones have a similar influence on heart function and metabolism, but this may occur in a differential manner and to a different extent In this study, the effects of norepinephrine (NE) and of triiodothyronine (T₃) were studied in regard to the function of the left (LV) and right ventricle (RV) and to the oxidative pentose phosphate pathway (PPP). NE was applied in rats as continuous i. v. infusion (0.2 mg/kg/h) for three days. T₃ was given as daily s.c. injections (0.2 mg/kg) for the same period of time. LV, and RV function was measured in the closed-chest trapanal-anesthetized animals using special Millar ultraminature catheter pressure transducers. NE induced an increase in heart rate, in mean arterial pressure, and in total peripheral resistance (TPR). The cardiac RNA/DNA and the left ventricular weight/body weight ratios were increased by about 40%. These effects were prevented by simultaneous -and -receptor blockade with prazosin and metoprolol, respectively, but not by verapamil which abolished the hemodynamic effects. RVSP was significantly elevated by NE in a dose-dependent manner. The functional effects of T₃ on the LV were not as pronounced as those induced by NE. Heart rate and LV dp/dt_max were increased by T₃ and this increase was prevented by concomitant -receptor blockade with, metoprolol. In contrast to NE, T₃ induced an increase in cardiac output and a concominant decrease in TPR. The RNA/DNA ratio was elevated and cardiac hypertrophy had developed after treatment for three days with T₃. These changes were not affected by -receptor blockade with metoprolol. RVSP was increased by T₃ to a lesser extent than with NE. In metabolic terms in turned out that only NE, but not T₃ had a stimulating effect on the cardiac PPP. NE increased the mRNA and activity of glucose-6-phosphate dehydrogenase (G-6-PD), the first and regulating enzyme of this pathway. However, there was no effect of T₃ on G-6-PD activity nor on 6-phosphogluconate dehydrogenase activity, one of the following enzymes in the pathway within the first 5 days of T₃ treatment. These results demonstrate that the functional effects of T₃ were not as pronounced as or even different from those of NE, and that T₃ lacked a stimulating effect on the cardiac PPP.     

Rapid recycling of triose phosphates in oak stem tissue

We report the carbon-13 and oxygen-18 isotope ratios in cellulose from the early and late wood of pedunculate oak (Quercus robur L.). The δ¹³ C value of the early wood correlates best with that of the late wood of the previous year. The δ¹⁸O value of the early wood correlates best with that of the late wood of the same year. We suggest that a biochemical explanation of these data is that there is a rapid cycle between hexose monophosphates and triose phosphates in oak stem tissue during cellulose synthesis. Evidence in support of this explanation is provided by the intramolecular distribution of ¹⁴C in labelled fructose extracted from cores of wood that had been supplied with [1?¹⁴C]- and [6-¹⁴C]glucose.     

内源无机磷酸盐对叶绿体Mg~（2＋）－ATP酶功能的调节

用ＳＴＮ（含蔗糖,０．４ｍｏｌ／Ｌ;ＮａＣｌ,０．０１ｍｏｌ／Ｌ和Ｔｒｉｓ－ＨＣｌ,０．０２ｍｏｌ／Ｌ,ｐＨ７．４）提取的菠菜叶片叶绿体再用ＳＴＮ洗涤后,它的内源无机磷酸盐含量急剧减少,其Ｍｇ２＋－ＡＴＰ酶水解ＡＴＰ的能力明显下降。进一步研究表明：叶绿体的内源无机磷酸盐含量减少会使反映叶绿体类囊体膜内外△ｐＨ变化的９－氨基吖啶的荧光猝灭减少,并加速光激活态ＡＴＰ酶的暗失活。     

Sucrose metabolism and fruit growth in parthenocarpic vs seeded blueberry (Vaccinium ashei) fruits

Although fruit set and development are induced by applications of gibberellins, final fruit weight of gibberellin-induced parthenocarpic fruit is often less than that of pollinated fruit. We examined changes in the activities of sucrose-metabolizing enzymes and sugar accumulation in developing fruits of cultivated blueberry (Vaccinium ashei Reade) and their correlation with fruit growth upon pollination or exogenous applications of gibberellic acid (GA₃). The objective was to determine if differences in fruit growth could be attributed to differences in enzyme activities and subsequent sugar accumulation in fruits. The fruit development period of GA₃-treated fruits was 15 days longer than that of pollinated fruits. At maturity, GA₃-treated fruit accumulated an average of 180 mg dry weight while pollinated fruit accumulated 390 mg dry weight. Dry weight accumulation in nonpollinated fruits was negligible and these fruits abscised by 45 days after bloom (DAB). The total carbon (C) cost (dry weight C + respiratory C) for fruit development was 109 and 244 mg C fruit^-1 for GA₃-treated and pollinated fruits, respectively. Hexose concentration increased to 100 mg (g fresh weight)^-1 at ripening in both GA₃-treated and pollinated fruits. Nonpollinated fruits reached a maximum hexose concentration at 45 DAB. Sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) activities reached a maximum of ≤5.0 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits. Soluble acid invertase (EC 3.2.1.26) activity increased to about 60 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits at ripening, while in nonpollinated fruits, a maximum soluble acid invertase activity of 0.12 μmol (g fresh weight)^-1 h^-1 was measured at 24 DAB. Insoluble acid invertase activity declined during the early stages of fruit growth and remained relatively low throughout fruit development. Neutral invertase activity was low throughout development, increasing to 5 μmol (g fresh weight)^-1 h^-1 at ripening in GA₃-treated and pollinated fruits. Our studies demonstrate that blueberry fruit development does not appear to be limited by sucrose metabolizing enzyme activity and/or the ability to accumulate sugars in either GA₃-treated or pollinated fruits.