Ontogenic profile of some antioxidants and lipid peroxidation in human placental and fetal tissues

Reactive oxygen species (ROS) pose a serious threat to maternal and fetal health during pregnancy. However, there is little information on the oxidative damage caused by ROS and its protection during prenatal life. The present study highlights the status of various antioxidants in human placental and fetal tissues at different phases of gestation. The activity profile of scavenging enzymes, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase as well as the concentrations of non-enzymatic antioxidants, ascorbic acid, -tocopherol, bilirubin and glutathione have been determined in human placental whole homogenate, placental brush border membrane and fetal liver over gestational periods ranging from 6 weeks of pregnancy till birth. The ontogenic profile of lipid peroxidation, a marker of oxidative damage has also been investigated in the feto-placental system. Catalase, superoxide dismutase and glutathione reductase activities increased significantly, but glutathione peroxidase activity remained almost the same throughout development. Except - tocopherol and bilirubin, the concentrations of other non-enzymic scavengers followed a significant increasing trend with advancement of pregnancy. Results indicate that there is gradual suppression of lipoperoxide formation with the progress of gestation to protect the fetus against oxygen toxicity.     

Modes of lactose uptake in the yeast species Kluyveromyces marxianus

Twelve lactose-assimilating strains of the yeast species Kluyveromyces marxianus and its varieties marxianus, lactis and bulgaricus were studied with respect to transport mechanisms for lactose, glucose and galactose, fermentation of these sugars and the occurrence of extracellular lactose hydrolysis. The strains fell into three groups. Group I (two strains): Fermentation of lactose, glucose and galactose, extracellular lactose hydrolysis, apparent facilitated diffusion of glucose and galactose; Group II (two strains): Lactose not fermented, glucose and galactose fermented and transported by an apparent proton symport, extracellular hydrolysis of lactose present (one strain) or questionable; Group III (eight strains): Lactose, glucose and galactose fermented, lactose transported by an apparent proton symport mechanism, extracellular hydrolysis of lactose and transport modes for glucose and galactose variable.     

Spectacles of migrant ‘illegality’: the scene of exclusion,the obscene of inclusion

Abstract

Border policing and immigration law enforcement produce a spectacle that enacts a scene of ‘exclusion’. Such spectacles render migrant ‘illegality’ visible. Thus, these material practices help to generate a constellation of images and discursive formations, which repetitively supply migrant ‘illegality’ with the semblance of an objective fact. Yet, the more these spectacles fuel anti-immigrant controversy, the more the veritable inclusion of the migrants targeted for exclusion proceeds apace. Their ‘inclusion’ is finally devoted to the subordination of their labour, which is best accomplished only insofar as their incorporation is persistently beleaguered with exclusionary campaigns that ensure that this inclusion is itself a form of subjugation. At stake, then, is a larger sociopolitical (and legal) process of inclusion through exclusion. This we may comprehend as the obscene of inclusion. The castigation of ‘illegals’ thereby supplies the rationale for essentializing citizenship inequalities as categorical differences that then may be racialized.     

Angiotensin II directly increases rabbit renal brush-border membrane sodium transport: Presence of local signal transduction system

Summary In the present study, we have examined the direct actions of angiotensin II (AII) in rabbit renal brush border membrane (BBM) where binding sites for AII exist. Addition of AII (10^–11–10^–7 m) was found to stimulate²²Na^– uptake by the isolated BBM vesicles directly. AII did not affect the Na⁺-dependent BBM glucose uptake, and the effect of AII on BBM²²Na⁺ uptake was inhibited by amiloride, suggesting the involvement of Na⁺/H⁺ exchange mechanism. BBM proton permeability as assessed by acridine orange quenching was not affected by AII, indicating the direct effect of AII on Na⁺/H⁺ antiport system.In search of the signal transduction mechanism, it was found that AII activated BBM phospholipase A₂ (PLA) and that BBM contains a 42-kDa guanine nucleotide-binding regulatory protein (G-protein) that underwent pertussis toxin (PTX)-catalyzed ADP-ribosylation. Addition of GTP potentiated, while GDP-ßS or PTX abolished, the effects of AII on BBM PLA and²²Na⁺ uptake, suggesting the involvement of G-protein in AII's actions. On the other hand, inhibition of PLA by mepacrine prevented AII's effect on BBM²²Na⁺ uptake, and activation of PLA by mellitin or addition of arachidonic acid similarly enhanced BBM²²Na⁺ uptake, suggesting the role of PLA activation in mediating AII's effect on BBM²²Na⁺ uptake.In summary, results of the present study show a direct stimulatory effect of AII on BBM Na⁺/H⁺ antiport system, and suggest the presence of a local signal transduction system involving G-protein mediated PLA activation.     

Localization-controlled specificity of FAD:threonine flavin transferases in Klebsiella pneumoniae and its implications for the mechanism of Na-translocating NADH:quinone oxidoreductase

The Klebsiella pneumoniae genome contains genes for two putative flavin transferase enzymes (ApbE1 and ApbE2) that add FMN to protein Thr residues. ApbE1, but not ApbE2, has a periplasm-addressing signal sequence. The genome also contains genes for three target proteins with the Dxx(s/t)gAT flavinylation motif: two subunits of Na⁺-translocating NADH:quinone oxidoreductase (Na⁺-NQR), and a 99.5 kDa protein, KPK_2907, with a previously unknown function. We show here that KPK_2907 is an active cytoplasmically-localized fumarate reductase. K. pneumoniae cells with an inactivated kpk_2907 gene lack cytoplasmic fumarate reductase activity, while retaining this activity in the membrane fraction. Complementation of the mutant strain with a kpk_2907-containing plasmid resulted in a complete recovery of cytoplasmic fumarate reductase activity. KPK_2907 produced in Escherichia coli cells contains 1 mol/mol each of covalently bound FMN, noncovalently bound FMN and noncovalently bound FAD. Lesion in the ApbE1 gene in K. pneumoniae resulted in inactive Na⁺-NQR, but cytoplasmic fumarate reductase activity remained unchanged. On the contrary, lesion in the ApbE2 gene abolished the fumarate reductase but not the Na⁺-NQR activity. Both activities could be restored by transformation of the ApbE1- or ApbE2-deficient K. pneumoniae strains with plasmids containing the Vibrio cholerae apbE gene with or without the periplasm-directing signal sequence, respectively. Our data thus indicate that ApbE1 and ApbE2 bind FMN to Na⁺-NQR and fumarate reductase, respectively, and that, contrary to the presently accepted view, the FMN residues are on the periplasmic side of Na⁺-NQR. A new, “electron loop” mechanism is proposed for Na⁺-NQR, involving an electroneutral Na⁺/electron symport. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

Free radical oxidation (autoxidation) of alkenones and other lipids in cells of Emiliania huxleyi

Cells of the coccolithophorid Emiliania huxleyi strain CS-57 grown under an atmosphere of air+0.5% CO(2) showed oxidative damage after 10 days growth with concomitant and major changes to the lipid composition. The fatty acid profile was strongly altered and lacked appreciable amounts of the polyunsaturated fatty acids (PUFA: C(18:5), C(18:3) and C(22:6)) typical of healthy cells. Oxidation products of these PUFA could not be detected, but monounsaturated fatty acids proved to be good indicators of oxidative processes. The presence (after NaBH(4)-reduction) of a high proportion of 11-hydroxyoctadec-cis-9-enoic and 8-hydroxyoctadec-cis-9-enoic acids showed that the degradation of oleic acid involved mainly free radical oxidation processes (70-75% autoxidation and 20-25% photooxidation). We also detected large amounts of degradation products of the oxidation product 9,10-epoxyoctadecanoic acid including diols, methoxyhydrins and chlorohydrins. These oxidative effects were found in all the lipid classes examined. Products included significant amounts of chlorophyll side-chain autooxidation products Z- and E-3,7,11,15-tetramethylhexadec-3-ene-1,2-diols and Z-and E-3,7,11,15-tetramethylhexadec-2-ene-1,4-diols, while phytyldiol was present in relatively low proportions. Delta(5)-3beta,7-epimeric unsaturated steroidal diols arising from the autooxidation of the Delta(5) double bond of epi-brassicasterol and minor amounts of Delta(4)-3beta,6-diols were also detected. Long-chain unsaturated ketone (alkenone) content per cell was much higher in the presence of 0.5% CO(2) likely due to carbon storage under these conditions. The proportions of di- and tri-unsaturated alkenones was relatively stable throughout the growth cycle in the absence of additional CO(2), but not when grown with 0.5% CO(2). The detection of characteristic alkenone autoxidation products in cells grown under these latter conditions allowed us to attribute the significant increase in index observed to the involvement of free radical oxidation processes.     

Phospholipid diversity: Correlation with membrane-membrane fusion events

The transport of various metabolically important substances along the endocytic and secretory pathways involves budding as well as fusion of vesicles with various intracellular compartments and plasma membrane. The membrane-membrane fusion events between various sub-compartments of the cell are believed to be mainly mediated by so-called “fusion proteins”. This study shows that beside the proteins, lipid components of membrane may play an equally important role in fusion and budding processes. Inside out (ISO) as well as right side out (RSO) erythrocyte vesicles were evaluated for their fusogenic potential using conventional membrane fusion assay methods. Both fluorescence dequenching as well as content mixing assays revealed fusogenic potential of the erythrocyte vesicles. Among two types of vesicles, ISO were found to be more fusogenic as compared to the RSO vesicles. Interestingly, ISO retained nearly half of their fusogenic properties after removal of the proteins, suggesting the remarkable role of lipids in the fusion process. In another set of experiments, fusogenic properties of the liposomes (subtilosome), prepared from phospholipids isolated from Bacillus subtilis (a lower microbe) were compared with those of erythrocyte vesicles. We have also demonstrated that various types of vesicles upon interaction with macrophages deliver encapsulated materials to the cytosol of the cells. Membrane-membrane fusion was also followed by the study, in which a protein synthesis inhibitor ricin A (that does not cross plasma membrane), when encapsulated in the erythrocyte vesicles or subtilosomes was demonstrated to gain access to the cytosol.     

Na+-independent l-arginine transport in rabbit renal brush border membrane vesicles

Na⁺-independent l-arginine uptake was studied in rabbit renal brush border membrane vesicles. The finding that steady-state uptake of l-arginine decreased with increasing extravesicular osmolality and the demonstration of accelerative exchange diffusion after preincubation of vesicles with l-arginine, but not d-arginine, indicated that the uptake of l-arginine in brush border vesicles was reflective of carrier-mediated transport into an intravesicular space. Accelerative exchange diffusion of l-arginine was demonstrated in vesicles preincubated with l-lysine and l-ornithine, but not l-alanine or l-proline, suggesting the presence of a dibasic amino acid transporter in the renal brush border membrane. Partial saturation of initial rates of l-arginine transport was found with extravesicular [arginine] varied from 0.005 to 1.0 mM. l-Arginine uptake was inhibited by extravesicular dibasic amino acids unlike the Na⁺-independent uptake of l-alanine, l-glutamate, glycine or l-proline in the presence of extravesicular amino acids of similar structure. l-Arginine uptake was increased by the imposition of an H⁺ gradient (intravesicular pH<extravesicular pH) and H⁺ gradient stimulated uptake was further increased by FCCP. These findings demonstrate membrane-potential-sensitive, Na⁺-independent transport of l-arginine in brush border membrane vesicles which differs from Na⁺-independent uptake of neutral and acidic amino acids. Na⁺-independent dibasic amino acid transport in membrane vesicles is likely reflective of Na⁺-independent transport of dibasic amino acids across the renal brush border membrane.     

Production of reactive oxygen species by photosystem II

Photosysthetic cleavage of water molecules to molecular oxygen is a crucial process for all aerobic life on the Earth. Light-driven oxidation of water occurs in photosystem II (PSII) — a pigment-protein complex embedded in the thylakoid membrane of plants, algae and cyanobacteria. Electron transport across the thylakoid membrane terminated by NADPH and ATP formation is inadvertently coupled with the formation of reactive oxygen species (ROS). Reactive oxygen species are mainly produced by photosystem I; however, under certain circumstances, PSII contributes to the overall formation of ROS in the thylakoid membrane. Under limitation of electron transport reaction between both photosystems, photoreduction of molecular oxygen by the reducing side of PSII generates a superoxide anion radical, its dismutation to hydrogen peroxide and the subsequent formation of a hydroxyl radical terminates the overall process of ROS formation on the PSII electron acceptor side. On the PSII electron donor side, partial or complete inhibition of enzymatic activity of the water-splitting manganese complex is coupled with incomplete oxidation of water to hydrogen peroxide. The review points out the mechanistic aspects in the production of ROS on both the electron acceptor and electron donor side of PSII.