Variable HCO 3 - affinity of Elodea canadensis Michaux in response to different HCO 3 - and CO2 concentrations during growth

Summary Elodea canadensis grows over a wide range of inorganic carbon, nutrient, and light conditions in lakes and streams. Affinity for HCO ₃ ^- use during photosynthesis ranged from strong to weak in Elodea collected from seven localities with different HCO ₃ ^- and CO₂ concentrations. The response to HCO ₃ ^- was also very plastic in plants grown in the laboratory at high HCO ₃ ^- concentrations and CO₂ concentrations varying from 14.8 to 2,200 M. Bicarbonate affinity was markedly reduced with increasing CO₂ concentrations in the growth medium so that ultimately HCO ₃ ^- use was not detectable. High CO₂ concentrations also decreased CO₂ affinity and induced high CO₂ compensation points (360M CO₂) and tenfold higher half-saturation values (800 M CO₂).The variable HCO ₃ ^- affinity is probably environmentally based. Elodea is a recently introduced species in Denmark, where it reproduces only vegetatively, leaving little opportunity for genetic variation. More important, local populations in the same water system had different HCO ₃ ^- affinities, and a similar variation was created by exposing one plant collection to different laboratory conditions.Bicarbonate use enabled Elodea to photosynthesize rapidly in waters of high alkalinity and enhanced the carbon-extracting capacity by maintaining photosynthesis above pH 10. On the other hand, use of HCO ₃ ^- represents an investment in transport apparatus and energy which is probably not profitable when CO₂ is high and HCO ₃ ^- is low. This explanation is supported by the findings that HCO ₃ ^- affinity was low in field populations where HCO ₃ ^- was low (0.5 and 0.9 m M) or CO₂ was locally high, and that HCO ₃ ^- affinity was suppressed in the laboratory by high CO₂ concentrations.Abbreviations DIC dissolved inorganic carbon (CO₂+ HCO ₃ ^- +CO ₃ ^- ) - CO₂ compensation point - K _1/2 apparent halfsaturation constant - P_{HCO 3} ^– interpolated photosynthesis in pure HCO ₃ ^- and zero CO₂ - P_max photosynthetic rate under carbon and light saturation     

Land plants of amphibious Littorella uniflora (L.) Aschers. maintain utilization of CO2 from the sediment

Summary Submerged macrophytes of the isoetid life form derive the majority of their CO₂ for photosynthesis from the sediment. The experiments described here were designed to test the hypothesis that root uptake of CO₂ is important also in the terrestrial form of Littorella uniflora. The results of ¹⁴CO₂ experiments showed that sediment CO₂ contributed 56% of the total fixation at 0.1mm CO₂ in the rhizosphere, 83% at 0.5mm and 96% at 2.5mm. Sediment CO₂ in emergent Littorella stands ranged from 0.1 to 1.0mm and averaged 0.5mm. Measurements of the net CO₂ exchange over the leaves showed an even higher dependence of the sediment as CO₂ source. Littorella leaves had no stomata at the base and densities (ca. 100 mm^–2) typical of terrestrial plants at the tip, allowing sediment-derived CO₂ to be supplied along the length of the leaf. The stomata permit supply of CO₂ from the air during periods of reduced sediment CO₂ concentrations (e.g. if the sediment dries up) and regulate transpiration.     

Legume-Rhizobium interactions: host induced alterations in capsular polysaccharides and infectivity of cowpea Rhizobia

Klebsiella aerogenes NCTC418 was cultured anaerobically under glucose-limited conditions in chemostat cultures at various growth rates, ranging from 0.13 h^-1 to 0.82 h^-1. It was found that the specific uptake rate of glucose varied linearly with the growth rate and that under these conditions glucose was fermented solely to acetate and ethanol plus CO₂+H₂ and formate.When steady-state cultures were pulsed with cell saturating concentrations of glucose, the specific glucose aptake rate increased immediately and substantially. However, at steady-state growth rates lower than 0.5 h^-1, this increase was not accompanied by a change in the growth rate, in contrast to cultures growing at higher rates. It was found that relief of the glucose limitation resulted in a shift in fermentation pattern: at the lower growth rates 50% or more of the extra glucose taken up was fermented to D-lactate.Incubation experiments with sonified cells revcaled that K. aerogenes possessed all the enzymes needed to convert dihydroxyacetone phosphate to methylglyoxal and subsequently to D-lactate, and that the rate at which this overall conversion occurred in vitro was in close agreement with the production rate of D-lactate in vivo. Moreover, it was found that the activities of the enzymes of the methylglyoxal bypass were dependent on the imposed growth rate. At higher growth rates, where cells possessed the potential to increase their growth rate immediately, the activity of methylglyoxal synthase was relatively low.it could be shown that, under low growth rate conditions, the uncoupling effect of the methylglyoxal bypass was highly effective and that, as a consequence thereof, a significant increase in the uptake rate of the energy source was accompanied by only a marginal increase in the rate at which ATP was synthesized.     

Aerobic electron transport in Propionibacterium shermanii effects of cyanide

Cyanide inhibited d- and l-lactate and NADH oxidase activities of membrane particles from Propionibacterium shermanii but only at relatively high concentrations. Inhibition occurred at two different sites in the electron transport pathway. One site, with a half-maximal inhibition concentration (I _0.5) of 2 to 3 mM KCN, is located at the terminal oxidase involved in cytochrome b oxidation; the evidence is consistent with cytochrome d being the major oxidase involved. At high concentrations, cyanide inhibited reduction of cytochrome b by d-lactate (I _0.5 value 20–25 mM cyanide). A proportion of the oxygen-uptake remained uninhibited even by 100 mM cyanide; this proportion was about 80% for succinate, 30% for l-lactate, 15% for d-lactate and 10% for NADH. The oxygen uptake per mol of substrate oxidised increased with increasing cyanide concentration and was accompanied by the formation of hydrogen peroxide as a product of a cyanide-insensitive oxidase system.Abbreviations PMS Phenazine methosulphate     

Characterisation of carbon dioxide and bicarbonate transport during steady-state photosynthesis in the marine cyanobacterium Synechococcus strain PCC7002

Net O₂ evolution, gross CO₂ uptake and net HCO _inf3 ^su– uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO₂ concentrations. Regardless of the CO₂ concentration during growth, all cells had the capacity to transport both CO₂ and HCO _inf3 ^su– ; however, the activity of HCO _inf3 ^su– transport was more than twofold higher than CO₂ transport even in cyanobacteria grown at high concentration of inorganic carbon (C_i = CO₂ + HCO _inf3 ^su– ). In low-C_i cells, the affinities of CO₂ and HCO _inf3 ^su– transport for their substrates were about 5 (CO₂ uptake) and 10 (HCO _inf3 ^su– uptake) times higher than in high-C_i cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated C_i pool reached 18, 32 and 55 mM in high-C_i, air-grown and low-C_i cells, respectively, when measured at 1 mM external C_i. Photosynthetic O₂ evolution, maximal CO₂ and HCO _inf3 ^su– transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO₂ provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO₂ concentrations. Transport studies with high-C_i cells revealed that CO₂ and HCO _inf3 ^su– uptake were equally inhibited when CO₂ fixation was reduced by the addition of glycolaldehyde. In contrast, in low-C_i cells steady-state CO₂ transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO₂ and HCO _inf3 ^su– uptake as well as O₂ evolution in both cell types. In high-C_i cells, the degree of inhibition was similar for HCO _inf3 ^su– transport and O₂ evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO₂ was much more sensitive to the inhibitor than HCO _inf3 ^su– transport, with an apparent I₅₀ value of around 250 M ethoxyzolamide for CO₂ uptake. The implications of our results are discussed with respect to C_i utilisation in the marine Synechococcus strain.Abbreviations Chl chlorophyll - C_i inorganic carbon (CO₂ + HCO _inf3 ^su– ) - CA carbonic anhydrase - CCM CO₂-concentrating mechanism - EZA ethoxyzolamide - GA glycolaldehyde - K_1/2 concentration required for half-maximal response - Rubisco ribulose-1,5,-bisphosphate carboxylase-oxygenase D.S. is a recipient of a research fellowship from the Deutsche Forschungsgemeinschaft (D.F.G.). In addition, we are grateful to Donald A. Bryant, Department of Molecular and Cell Biology and Center of Biomolecular Structure Function, Pennsylvania State University, USA, for sending us the wild-type strain of Synechococcus PCC7002.     

Molar growth yields,respiration and cytochrome profiles of Beneckea natriegens when grown under carbon limitation in a chemostat

The effect of growth rate on the physiology of Beneckea natriegens was studied in chemostat culture. The molar growth yields (Y) from glucose and oxygen, the specific rates of oxygen (q _{O 2}) and glucose (q _glc) consumption and the specific rate of CO₂ production (q _{CO 2}) were linearly dependent on the growth rate over the dilution rate 0.17 h^-1 to 0.60 h^-1. Further increase in the dilution rate resulted in a decrease in growth yield and respiration rate and these changes were coincident with increases in the specific rate of glucose utilisation and of acetate production. The affinity of Beneckea natriegens for glucose was similar when measured either directly in chemostat culture or in a closed oxygen electrode system using harvested bacteria. The total content of cytochromes decreased with increasing growth rate. However, the quantity of CO-binding cytochromes remained independent of growth rate and correlated with the potential respiration rate.     

Pathway of propionate formation in Desulfobulbus propionicus

Whole cells of Desulfobulbus propionicus fermented [1-¹³C]ethanol to [2-¹³C] and [3-¹³C]propionate and [1-¹³C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA: pyruvate transacetylase, acetase kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activity of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence of pyruvate, CoA and ATP and the oxaloacetate-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor.The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.Abbreviations DCPIP 2,6-dichlorophenolindophenol - PEP phosphoenolpyruvate     

Inorganic-carbon uptake by the marine diatom Phaeodactylum tricornutum

Air-grown cells of the marine diatom Phaeodactylum tricornutum showed only 10% of the carbonic-anhydrase activity of air-grown Chlamydomonas reinhardtii. Measurement of carbonic-anhydrase activity using intact cells and cell extracts showed all activity was intracellular in Phaeodactylum. Photosynthetic oxygen evolution at constant inorganic-carbon concentration but varying pH showed that exogenous CO₂ was poorly utilized by the cells. Sodium ions increased the affinity of Phaeodactylum for HCO ₃ ^- and even at high HCO ₃ ^- concentrations sodium ions enhanced HCO ₃ ^- utilization. The internal inorganic-carbon pool (HCO ₃ ^- +CO₂] was measured using a silicone-oil-layer centrifugal filtering technique. The internal [HCO ₃ ^- +CO₂] concentration never exceeded 15% of the external [HCO ₃ ^- +CO₂] concentration even at the lowest external concentrations tested. It is concluded that an internal accumulation of inorganic carbon relative to the external medium does not occur in P. tricornutum.Abbreviation Hepes 4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid     

Treponema succinifaciens sp. nov., an anaerobic spirochete from the swine intestine

The morphology, the general physiological characteristics, and the energy-yielding metabolism of an obligately anaerobic spirochete isolated from the colon of a swine were studied. Electron microscopy showed that the helical spirochetal cells possessed an outer sheath, a protoplasmic cylinder, and 4 periplasmic fibrils in a 2-4-2 arrangement. The spirochete grew in an atmosphere of N₂ in prereduced media containing a carbohydrate, NaHCO₃, rumen fluid, yeast extract, peptone, l-cysteine, and inorganic salts. The spirochete fermented carbohydrates and required substrate amounts of CO₂ (HCO ₃ ^- ) for growth. Amino acids were not fermented. Major fermentation products of cells growing with glucose as the substrate and in the presence of CO₂ were acetate, formate, succinate, and lactate. Small amounts of 2,3-butanediol, pyruvate, and acetoin were also formed. Determinations of enzymatic activities in cell extracts, and of radioactivity in products formed by growing cells from [1-¹⁴C]glucose, indicated that this sugar was dissimilated to pyruvate via the Embden-Meyerhof pathway. The spirochetes used a coliform-type clastic reaction to metabolize pyruvate. Determinations of radioactivity in products formed from [¹⁴C]NaHCO₃ indicated that CO₂ was assimilated and used in succinate production. The guanine+cytosine content of the DNA was 36 mol%. This study indicates that this intestinal spirochete represents a new species of Treponema. It is proposed that the new species be named Treponema succinifaciens.Abbreviations cpm counts per minute - DTT dithiothreitol - EM Embden-Meyerhof - GC guanine plus cytosine - IgG immunoglobulin G - PC protoplasmic cylinder - PF periplasmic fibrils (axial fibrils) - OS outer sheath     

pHi regulation in Ehrlich mouse ascites tumor cells: Role of sodium-dependent and sodium-independent chloride-bicarbonate exchange

pH _i recovery in acid-loaded Ehrlich ascites tumor cells and pH _i maintenance at steady-state were studied using the fluorescent probe BCECF.Both in nominally HCO ₃ ^– -free media and at 25 mm HCO ₃ ^– , the measured pH _i (7.26 and 7.82, respectively) was significantly more alkaline than the pH _i . value calculated assuming the transmembrane HCO ₃ ^– gradient to be equal to the Cl^– gradient. Thus, pH _i in these cells is not determined by the Cl^– gradient and by Cl^–/HCO ₃ ^– exchange.pH _i recovery following acid loading by propionate exposure, NH ₄ ⁺ withdrawal, or CO₂ exposure is mediated by amiloride-sensitive Na⁺/H⁺ exchange in HCO₃ ^– free media, and in the presence of HCO ₃ ^– (25 mm) by DIDS-sensitive, Na⁺-dependent Cl^–/HCO ₃ ^– exchange. A significant residual pH _i recovery in the presence of both amiloride and DIDS suggests an additional role for a primary active H⁺ pump in pH _i regulation. pH _i maintenance at steady-state involves both Na⁺/H⁺ exchange and Na⁺-dependent Cl^–/HCO ₃ ^– exchange.Acute removal of external Cl^– induces a DIDS-sensitive, Na⁺-dependent alkalinization, taken to represent HCO ₃ ^– influx in exchange for cellular Cl^–. Measurements of ³⁶Cl^– efflux into Cl^–-free gluconate media with and without Na⁺ and/or HCO ₃ ^– (10 mm) directly demonstrate a DIDS-sensitive, Na⁺ dependent Cl^–/HCO ₃ ^– exchange operating at slightly acidic pH _i (pH_o 6.8), and a DIDS-sensitive, Na⁺-independent Cl^–/HCO ₃ ^– exchange operating at alkaline pH _i (pH _o 8.2).The excellent technical assistance of Marianne Schiødt and Birgit B. Jørgensen is gratefully acknowledged. The work was supported by the Carlsberg Foundation (B.K.) and by a grant from the Danish Natural Science Foundation (E.K.H. and L.O.S.).     

Betaine Tripled the Volumetric Productivity of d(-)-lactate by Escherichia coli Strain SZ132 in Mineral Salts Medium

Osmotic stress restricts glycolytic flux, growth (rate and yield), d-lactate productivity, and d-lactate tolerance in Escherichia coli B strain SZ132 during batch fermentation in mineral salts medium with 10% (w/v) sugar. Addition of 1 mm betaine, a non-metabolized protective osmolyte, doubled cell yield, increased specific productivity of d-lactate and glycolytic flux by 50%, and tripled volumetric productivity (from 8.6 to 25.7 mmol l⁻¹ h⁻¹; 0.8 to 2.3 g l⁻¹ h⁻¹). Glycolytic flux and specific productivity in mineral salts medium with betaine exceeded that in Luria broth, substantially eliminating the need for complex nutrients during d-lactate production. In mineral salts medium supplemented with betaine, SZ132 produced approximately 1 mol d-lactate (90 g) per 100 g sugar (glucose or sucrose). Revisions requested 17 January 2006; Revisions received 7 February 2006     

Evidence for an anion exchanger in the mouse lacrimal gland acinar cell membrane

Summary Anion exchange transport in the mouse lacrimal gland acinar cell membrane was studied by measuring the intracellular H⁺ (pH_i) and Cl^– (aCl_i) activities with double-barreled ion-selective microelectrodes. In a HCO ₃ ^– -free solution of pH 7.4 (HEPES/Tris buffered), pH_i was 7.25 andaCl_i was 33mm. By an exposure to a HCO ₃ ^– (25mm HCO ₃ ^– /5% CO₂, pH 7.4) solution for 15 min,aCl_i was decreased to 25mm and pH_i was transiently decreased to about 7.05 within 1 min, then slowly relaxed to 7.18 in 15 min. Intracellular HCO ₃ ^– concentration [HCO ₃ ^– ]_i, calculated by the Henderson-Hasselbalch's equation, was 11mm at 1 min after the exposure and then slowly increased to 15mm. Readmission of the HCO ₃ ^– -free solution reversed the changes inaCl_i and pH_i. The intracellular buffering power was about 40mm/pH. An addition of DIDS (0.2mm) significantly inhibited the rates of change inaCl_i, pH_i, and [HCO ₃ ^– ]_i caused by admission/withdrawal of the HCO ₃ ^– , solution and decreased the buffer value. Replacement of all Cl^– with gluconate in the HCO ₃ ^– solution increased pH_i, and readmission of Cl^– decreased pH_i. The rates of these changes in pH_i were reduced by DIDS by 32–45% but not by amiloride (0.3mm). In the HCO ₃ ^– solution, a stimulation of intracellular HCO ₃ ^– production by exposing the tissue to 25mm NH ₄ ⁺ increasedaCl_i significantly. While in the HCO ₃ ^– -free solution or in the HCO ₃ ^– , solution containing DIDS, exposure to NH ₄ ⁺ had little effect onaCl_i. All of these findings were consistent with the presence of a reversible, disulfonic stilbene-sensitive Cl^–/HCO ₃ ^– exchanger in the basolateral membrane of the acinar cells. The possibility of anion antiport different from one-for-one Cl^–/HCO ₃ ^– exchange is discussed.     

pH Regulation in tissue-cultured bovine lens epithelial cells

Summary The intracellular pH (pH _i ) of tissue-cultured bovine lens epithelial cells was measured in small groups of 6 to 10 cells using the trapped fluorescent dye 2,7-bis-(2-,carboxyethyl)-5 (and 6)carboxyfluorescein (BCECF). When perifused at 35°C with artificial aqueous humour solution (AAH) containing 16 mM HCO ₃ ^- and 5% CO₂, pH 7.25, pH _i was 7.19±0.02 (sem, n = 95). On removing HCO ₃ ^- and CO₂ there was an initial transient alkalinization followed by a fall in pH to a steady value of 6.97±0.03 (sem, n = 54). Addition of 0.25 mM 4,4-diisothiocyanatostilbene2, 2-disulfonic acid (DIDS) to AAH containing HCO ₃ ^- and CO₂ led to a rapid and pronounced fall in pH. Exposure to Na⁺-free AAH again led to a marked fall in pH _i , but in this case the addition of DIDS did not produce a further fall. Substitution of the impermeant anion gluconate for Cl^– in the presence of HCO ₃ ^- led to a rise in pH _i , while substitution in the absence of HCO ₃ ^- led to a fall in pH _i . The above data indicate a significant role for a sodium-dependent Cl^–-HCO ₃ ^- exchange mechanism in the regulation of pH _i . Addition of 1 mM amiloride to control AAH in both the presence and absence of HCO ₃ ^- led to a marked fall in pH _i , indicating that a Na⁺/H⁺ exchange mechanism also has a significant role in the regulation of pH _i . There is evidence for a lactic acid transport mechanism in bovine lens cells, as addition of lactate to the external medium produced a rapid fall in pH _i . Larger changes in pH _i were observed in control compared to HCO ₃ ^- -free AAH and in the latter case a pronounced alkalinizing overshoot was obtained on removing external lactate. Tissue-cultured bovine lens cells thus possess at least three membrane transport mechanisms that are involved in pH regulation. The buffering capacity of the lens cells was measured by perturbing pH _i with either NH ₄ ⁺ or procaine. The values obtained were similar in both cases and the intrinsic buffering capacity measured in the absence of external HCO ₃ ^- was 5 mm/pH unit (procaine). However, in the presence of HCO ₃ ^- and CO₂ the buffer capacity increases approximately fourfold, indicating that HCO ₃ ^- is the principal intracellular buffer.We acknowledge financial support from the Wellcome Trust and the Humane Research Trust for this project. M.R. Williams was in receipt of a Science & Engineering Research Council studentship.     

Effects of nitrogen supply and elevated carbon dioxide on construction cost in leaves of Pinus taeda (L.) seedlings

Seedlings of loblolly pine (Pinus taeda L.) were grown under varying conditions of soil nitrogen and atmospheric carbon dioxide availability to investigate the interactive effects of these resources on the energetic requirements for leaf growth. Increasing the ambient CO₂ partial pressure from 35 to 65 Pa increased seedling growth only when soil nitrogen was high. Biomass increased by 55% and photosynthesis increased by 13% after 100 days of CO₂ enrichment. Leaves from seedlings grown in high soil nitrogen were 7.0% more expensive on a g glucose g^–1 dry mass basis to produce than those grown in low nitrogen, while elevated CO₂ decreased leaf cost by 3.5%. Nitrogen and CO₂ availability had an interactive effect on leaf construction cost expressed on an area basis, reflecting source-sink interactions. When both resources were abundant, leaf construction cost on an area basis was relatively high (81.8±3.0 g glucose m^–2) compared to leaves from high nitrogen, low CO₂ seedlings (56.3±3.0 g glucose m^–2) and low nitrogen, low CO₂ seedlings (67.1±2.7 g glucose m^–2). Leaf construction cost appears to respond to alterations in the utilization of photoassimilates mediated by resource availability.     

Formation of d(-)-1,2-propanediol and d(-)-lactate from glucose by Clostridium sphenoides under phosphate limitation

Clostridium sphenoides was grown on glucose in a phosphate-limited medium. Below 80 M phosphate two new products were formed in addition to ethanol, acetate, H₂ and CO₂: d(-)-1,2-propanediol and d(-)-lactate. These compounds were apparently synthesized via the methylglyoxal by-pass. The activity of the enzymes involvedmethylglyoxal synthase, methylglyoxal reductase, 1,2-propanediol dehydrogenase and glyoxalase-could be demonstrated in cell extracts of C. sphenoides. The formation of 1,2-propanediol from methylglyoxal proceeded via lactaldehyde. The enzyme methylgloxal synthase was inhibited by phosphate. Clostridium glycolicum, C. nexile, C. cellobioparum, C. oroticum and C. indolis did not produce propanediol under the condition of phosphate limitation. The latter two species, however, formed d(-)-lactate.Dedicated to Prof. Dr. G. Drews on the occasion of his 60th birthday     

The presence of glycollate oxidase and dehydrogenase in Dunaliella primolecta

Homogenates of Dunaliella primolecta, D. salina and D. tertiolecta were assayed for glycollate oxidase and glycollate dehydrogenase. Both D. primolecta and D. salina but not D. tertiolecta showed substantial glycollate-dependent O₂-uptake which is characteristic of glycollate oxidase. L-Lactate was an alternative substrate and both glycollate- and L-lactate-dependent O₂ uptake were insensitive to 2 mM cyanide. Glycollate dehydrogenase, measured by following the glycollate-dependent reduction of 2,6-dichlorophenolindophenol under aerobic conditions, was present in D. primolecta, D. salina and D. tertiolecta. In the presence of glycollate and D-lactate, rates were additive so both glycollate and D-lactate dehydrogenases are present in the homogenates. Glycollate and D-lactate oxidation were both inhibited by 2 mM cyanide. Organelles released from phototrophically grown cells of D. primolecta were separated by isopycnic centrifugation on sucrose gradients. Glycollate oxidase was present in the peroxisome fraction at an equilibrium density of 1.25 g/cm³, while the major peak of glycollate dehydrogenase activity was in the mitochondrial fraction at an equilibirium density of 1.22 g/cm³.     

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments

Colony counts of acetate-, propionate- and l-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers.Anaerobic mineralization of acetate, propionate and l-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. l-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria, belonging to the species Desulfovibrio desulfuricans, and lactate-fermenting bacteria were found in approximately equal amounts in the sediments. Acetate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, l-lactate and ethanol were oxidized with concomitant sulfate reduction. l-Lactate and pyruvate could be fermented by most of the isolated strains.     

Effect of dissolved inorganic carbon on the expression of carboxysomes,localization of Rubisco and the mode of inorganic carbon transport in cells of the cyanobacterium Synechococcus UTEX 625

In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO₂+HCO _inf3 ^sup- ) in the growth medium. In cells grown under 5% CO₂ and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section^-1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 l CO₂ · 1^-1 possessed many carboxysomes (>8 · longitudinal section^-1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO _inf3 ^sup- transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon (CO₂+HCO _inf3 ^sup- +CO _inf3 ^sup2- ) - PRK phosphoribulokinase - RuBP ribulose 1,5-bisphosphate - Rubisco LS large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase     

Isolation and characterization of peroxisomes from diatoms

Peroxisomes were isolated by gradient centrifugation from two different diatoms: Nitzschia laevis (subgroup of Pennales) and Thalassiosira fluviatilis (subgroup of Centrales). In neither of these organelles could catalase or any H₂O₂-forming oxidase be demonstrated. The glycolate-oxidizing enzyme present in the peroxisomes is a dehydrogenase capable of oxidizing l-lactate as well. The peroxisomes also contain the glyoxysomal markers isocitrate lyase and malate synthase. However, enzymes of the fatty-acid -oxidation pathway are located exclusively in the mitochondria. The mitochondria additionally possess glutamate-glyoxylate aminotransferase and a glycolate dehydrogenase which differs from the peroxisomal glycolate dehydrogenase since it preferably utilizes d-lactate as an alternative substrate. Hydroxypyruvate reductase and glyoxylate carboligase were not found in the cells of either diatom. By culturing Nitzschia laevis it could be demonstrated that decreasing the CO₂ concentration in the aeration mixture from 2% to 0.03% and increasing the irradiance from 40 to 250 mol quanta · m^–2 · s^–1 resulted in an increase of all peroxisomal enzyme activities. In addition, enzyme activities of the -oxidation pathway were increased. However, mitochondrial glycolate dehydrogenase and aminotransferase did not alter their activities under these conditions. Summarizing all results, it is postulated that there are two different pathways for the metabolism of glycolate in the diatoms.This work was supported by the Deutsche Forschungsgemeinschaft.     

Effects of salicylate on HCO 3 − /Cl− exchange across the human erythrocyte membrane

Summary Changes in extracellular pH (pH _o ) in human red cell suspensions were monitored in a stopped-flow rapid reaction apparatus. A 20% suspension of washed human RBC in saline at pH 7 containing NaHCO₃ and extracellular carbonic anhydrase was mixed with an equal volume of buffered saline solution at pH 6.7. Sodium salicylate, when present, was added to both the erythrocyte suspension and the buffer solution. The effects of salicylate in the therapeutic to toxic concentration range on HCO ₃ ^– /Cl^– exchange were studied at 37°C. HCO ₃ ^– /Cl^– exchange flux was estimated using the extracellular buffer capacity and the difference betweendpH _o /dt using a control RBC suspension and that using a suspension of RBC whose anion exchange pathway was markedly inhibited. The results show that salicylate competitively decreases the rate of HCO ₃ ^– /Cl^– exchange, with inhibition increasing as salicylate concentration increases.K _I is 2.4mm. At a salicylate concentration of 10mm, HCO ₃ ^– /Cl^– exchange under the conditions of our experiments was inhibited by more than 70%. These findings are consistent with the possibility that CO₂ transfer in capillary bedsin vivo may be diminished in the presence of salicylate due to slowing of red cell HCO ₃ ^– /Cl^– exchange.