Respiratory rates in the cladoceran Ceriodaphnia dubia in Lake Rotongaio, a monomictic lake

The experimentally measured oxygen consumption rate by the cladoceran,Ceriodaphnia dubia, showed a linear increase between 5 and 20°C.Oxygen consumption rates of C. dubia were estimated in situfrom respiratory electron transport system (ETS) activity inLake Rotongaio during summer stratification and winter mixing.Oxygen consumption was 0.002 µl O₂ animal^–1 h^–1in the hypolimnion and 0.076 µl O₂ animal^–1 h^–1in the epilimnion during stratification. Implications of respiredoxygen for metabolic carbon requirements are discussed.     

Plankton community respiration in Bransfield Strait (Antarctic Ocean) during austral spring

Community respiration (R) was determined in Bransfield Straitfrom oxygen changes in water samples incubated in borosilicatebottles maintained at in situ temperature. The respiratory electrontransport system (ETS) activity of seawater communities wasalso measured from the same samples. Both data sets were relatedby the regression equation: log R (mg O₂ m^–3 day^–1)=0.462+0.730xlogETS activity mg O₂ m^–3 day^–1) (r=0.80, n=23). Fromthis equation and 37 ETS activity depth profiles, we calculatedthe integrated (0–100 m) community respiration as beingin the range 1.2–4.5 g O₂ m^–2 day^–1 (mean=2.2).These values do not differ significantly from other publishedresults for the Arctic and Antarctic Oceans. Assuming a respiratoryquotient of unity, the areal respiration ranges between 0.45and 1.69 g C m^–2 day^–1 (mean=0.8). This would representan important sink for the primary production reported for BransStrait. The spatial distribution of community respiration showedhigher values associated with the warmer and phytoplankton-richwaters outflowing from Gerlache Strait into Bransfield Strait,and with the front that separates Bellingshausen Sea watersfrom Weddell Sea waters. We suggest that this pattern of distributionmay be related to the transport of organic matter by the BransfieldCurrent along the front.     

Respiration and respiratory electron transport activity in marine phytoplankton: growth rate dependence and light enhancement

Respiratory electron transport system (ETS) activity and actualoxygen consumption rates were measured in batch cultures offour species of marine phytoplankton, in two different growthstages: exponential or log-phase (L) and stationary phase (S).The L cultures showed higher ETS activity and respiration ratesthan the S cultures of the same species. Among the L cultures,the higher respiration and ETS activity corresponded to thosehaving higher growth rates. The carbon-specific ETS activityand the carbon-specific respiration (h^–1) showed a cleardependence on growth rates. Samples subjected to short (10 min)exposures to high, oversaturating irradiances (1000 µEm^–2 s^–1) displayed enhanced ETS activity and respiration.The experiments show that, under the light regime at which thealgal cells grow, the respiratory ETS activity and actual oxygenconsumption in phytoplankton are strongly related to growthrate and that short, high irradiance exposures enhance boththe respiratory enzyme activity and their actual oxygen consumption.     

Glucosamine inhibits angiotensin II-induced cytoplasmic Ca2+ elevation in neonatal cardiomyocytes via protein-associated O-linked N-acetylglucosamine

We previously reported that glucosamine and hyperglycemia attenuate the response of cardiomyocytes to inositol 1,4,5-trisphosphate-generating agonists such as ANG II. This appears to be related to an increase in flux through the hexosamine biosynthesis pathway (HBP) and decreased Ca²⁺ entry into the cells; however, a direct link between HBP and intracellular Ca²⁺ homeostasis has not been established. Therefore, using neonatal rat ventricular myocytes, we investigated the relationship between glucosamine treatment; the concentration of UDP-N-acetylglucosamine (UDP-GlcNAc), an end product of the HBP; and the level of protein O-linked N-acetylglucosamine (O-GlcNAc) on ANG II-mediated changes in intracellular free Ca²⁺ concentration ([Ca²⁺]_i). We found that glucosamine blocked ANG II-induced [Ca²⁺]_i increase and that this phenomenon was associated with a significant increase in UDP-GlcNAc and O-GlcNAc levels. O-(2-acetamido-2-deoxy-D-glucopyranosylidene)-amino-N-phenylcarbamate, an inhibitor of O-GlcNAcase that increased O-GlcNAc levels without changing UDP-GlcNAc concentrations, mimicked the effect of glucosamine on the ANG II-induced increase in [Ca²⁺]_i. An inhibitor of O-GlcNAc-transferase, alloxan, prevented the glucosamine-induced increase in O-GlcNAc but not the increase in UDP-GlcNAc; however, alloxan abrogated the inhibition of the ANG II-induced increase in [Ca²⁺]_i. These data support the notion that changes in O-GlcNAc levels mediated via increased HBP flux may be involved in the regulation of [Ca²⁺]_i homeostasis in the heart. hypertrophy; left ventricle; calcium channels; calcium signaling     

Hydrogen Effect on Nitrogenase (C2H2 Reduction) Response to Oxygen in Bradyrhizobium japonicum-Phaseoleae Symbioses

The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup⁺ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO₂, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO₂, nitrogenaseactivity of Hup⁺ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO₂ for ARA (COP), from 35.3 to 40.3 kPa O₂, and the ARA atsupraoptimal pO₂; at suboptimal PO₂ there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H₂ effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O₂ limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata     

Characterization and Induction of the Activity of 1-Aminocyclopropane-1-Carboxylate Oxidase in the Wounded Mesocarp Tissue of Cucurbita maxima

1-Aminocyclopropane-1-carboxylate (ACC) oxidase (ethylene-formingenzyme) was isolated from wounded mesocarp tissue of Cucurbitamaxima (winter squash) fruit, and its enzymatic properties wereinvestigated. The enzyme required Fe²⁺ and ascorbate for itsactivity as well as ACC and O₂ as substrates. The in vitro enzymeactivity was enhanced by CO₂. The apparent K_m value for ACCwas 175 µM under atmospheric conditions. The enzyme activitywas inhibited by sulfhydryl inhibitors and divalent cationssuch as Co²⁺, Cu²⁺, and Zn²⁺. ACC oxidase activity was induced at a rapid rate by woundingin parallel with an increase in the rate of ethylene production.The exposure of excised discs of mesocarp to 2,5-norbornadiene(NBD),an inhibitor of ethylene action, strongly suppressed inductionof the enzyme, and the application of ethylene significantlyaccelerated the induction of the activity of ACC oxidase inthe wounded mesocarp tissue. These results suggests that endogenousethylene produced in response to wounding may function in promotingthe induction of ACC oxidase. (Received January 13, 1993; Accepted April 15, 1993)     

Ammonia Uptake in the Alkalophilic Cyanobacterium Spirulina platensis

Ammonia uptake was studied in the alkalophilic cyanobacteriumSpirulina platensis. In continuous cultures under optimal growthconditions ammonia supported optimal growth (doubling time of9.3 h), causing a reduction of glutamine synthetase activityto 25% of that found in cultures grown on NO₃. Long term (20min) ammonia uptake assays were performed to study the dependencyon metabolism: 1) Ammonia uptake proceeded at the same ratesin the light and in the dark, the pH dependency pattern correlatingwith light-dependent O₂ evolution and dark O₂ consumption. 2)The uptake of ammonia was pH dependent with an optimum at pH9.3. 3) The uptake was totally dependent upon the activity ofglutamine synthetase and was completely inhibited by methoininesulfoximine. To study the mechanism by which NH₄⁺/NH₃ enters the cells, shortterm experiments (up to 1 min) were performed at pH 7.0 andpH 10.0: At pH 7.0 the uptake was slow and at a constant rate.At pH 10.0, the uptake did not saturate even at 1 mM ammoniaand the kinetics were biphasic, consisting of a fast componentlasting less than 5 seconds and of a subsequent slower component.The fast phase was insensitive to methionine sulfoximine, whereasthe slower phase was completely inhibited by this compound.We suggest that under optimal (alkaline) pH the entry of ammoniainto Spirulina cells is likely to be a pH driven diffusion process,continuously supported by its intracellular assimilation. ¹Contribution number 35 of the Microalgal Biotechnology Laboratory. (Received September 19, 1988; Accepted January 16, 1989)     

Photoregulation of Respiratory Activity in the Cyanophyte Synechocystis PCC 6714: the Possibility of the Simultaneous Regulation of the Amount of PS I Complex and the Activity of Respiratory Terminal Oxidase in Thylakoids

Respiration of the cyanophyte Synechocystis PCC 6714 was studiedin relation to conditions for cell growth. Under our experimentalconditions, the KCN-sensitive O₂-uptake observed with intactcells was found to be limited at the step catalyzed by the terminaloxidase in thylakoids, indicating that the activity of O₂-uptakeby intact cells corresponds to that of the terminal oxidasein thylakoids. The activity was found to be variable dependingon the growth conditions; it was higher under conditions wherethe level of PS I, another terminal component of the thylakoidelectron transport system (ETS) was elevated, whereas it waslower under conditions where the level of PS I was reduced.Changes in the activity did not occur when protein synthesiswas suppressed by chloramphenicol. The results suggest that,similarly to the regulation of levels of PS I, the activityor the amount of terminal oxidase in thylakoids is regulatedin response to the redox steady-state of intermediate component(s)of ETS, in order to maintain a balance between the efflux ofelectrons from the ETS and the influx to the ETS. ¹Present address: P.G. Department of Botany, Utkal University,Bhubaneswar-751004, Orissa, Keonjhar, India (Received September 27, 1989; Accepted March 22, 1990)     

Large-conductance calcium-activated potassium channel activity is absent in human and mouse neutrophils and is not required for innate immunity

Large-conductance Ca²⁺-activated K⁺ (BK) channels are reported to be essential for NADPH oxidase-dependent microbial killing and innate immunity in leukocytes. Using human peripheral blood and mouse bone marrow neutrophils, pharmacological targeting, and BK channel gene-deficient (BK^–/–) mice, we stimulated NADPH oxidase activity with 12-O-tetradecanoylphorbol-13-acetate (PMA) and performed patch-clamp recordings on isolated neutrophils. Although PMA stimulated NADPH oxidase activity as assessed by O₂^– and H₂O₂ production, our patch-clamp experiments failed to show PMA-activated BK channel currents in neutrophils. In our studies, PMA induced slowly activating currents, which were insensitive to the BK channel inhibitor iberiotoxin. Instead, the currents were blocked by Zn²⁺, which indicates activation of proton channel currents. BK channels are gated by elevated intracellular Ca²⁺ and membrane depolarization. We did not observe BK channel currents, even during extreme depolarization to +140 mV and after elevation of intracellular Ca²⁺ by N-formyl-L-methionyl-L-leucyl-phenylalanine. As a control, we examined BK channel currents in cerebral and tibial artery smooth muscle cells, which showed characteristic BK channel current pharmacology. Iberiotoxin did not block killing of Staphylococcus aureus or Candida albicans. Moreover, we addressed the role of BK channels in a systemic S. aureus and Yersinia enterocolitica mouse infection model. After 3 and 5 days of infection, we found no differences in the number of bacteria in spleen and kidney between BK^–/– and BK^+/+ mice. In conclusion, our experiments failed to identify functional BK channels in neutrophils. We therefore conclude that BK channels are not essential for innate immunity. killing assay; reactive oxygen species; BK-deficient mice; mice infection     

Nitric oxide attenuates IGF-I-induced aortic smooth muscle cell motility by decreasing Rac1 activity: essential role of PTP-PEST and p130cas

Recent data support the hypothesis that reactive oxygen species (ROS) play a central role in the initiation and progression of vascular diseases. An important vasoprotective function related to the regulation of ROS levels appears to be the antioxidant capacity of nitric oxide (NO). We previously reported that treatment with NO decreases phosphotyrosine levels of adapter protein p130^cas by increasing protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein (PTP-PEST) activity, which leads to the suppression of agonist-induced H₂O₂ elevation and motility in cultured rat aortic smooth muscle cells (SMCs). The present study was performed to investigate the hypotheses that 1) IGF-I increases the activity of the small GTPase Rac1 as well as H₂O₂ levels and 2) NO suppresses IGF-I-induced H₂O₂ elevation by decreasing Rac1 activity via increased PTP-PEST activity and dephosphorylation of p130^cas. We report that IGF-I induces phosphorylation of p130^cas and activation of Rac1 and that NO attenuates these effects. The effects of NO are mimicked by the overexpression of PTP-PEST or dominant-negative (dn)-p130^cas and antagonized by the expression of dn-PTP-PEST or p130^cas. We conclude that IGF-I induces rat aortic SMC motility by increasing phosphotyrosine levels of p130^cas and activating Rac1 and that NO decreases motility by activating PTP-PEST, inducing dephosphorylating p130^cas, and decreasing Rac1 activity. Decreased Rac1 activity lowers intracellular H₂O₂ levels, thus attenuating cell motility. hydrogen peroxide; protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein; p130^cas     

Translocation Profiles of [11C] and [13N]-Labelled Metabolites after Assimilation of 11CO2 and [13N]-Labelled Ammonia Gas by Leaves of Helianthus annuus L. and Lupinus albus L.

Tracer amounts of atmospheric [¹³N]-Iabelled ammonia gas, wereabsorbed by leaves of Lupinus albus and Helianthus annuus inboth the light and the dark. Exogenous [¹³N]-ammonia was onlyabsorbed in the dark when the feeding occurred shortly aftera period of illumination and the tissue was not depleted ofits carbohydrate reserves (e.g. starch). Incorporation of the[¹³N]-ammonia appeared to occur via the leaf glutamine synthetase/glutamatesynthase (GS/GOGAT) cycle since 2.0 mol m^–3 MSX, an inhibitorof the GS reduced uptake in both the light and dark. Photosyntheticincorporation of ¹¹CO₂ was not affected by this treatment Therate of movement of [¹³N]-assimilates in the petiole of attachedleaves of Helianthus and Lupinus was similar to that of the¹¹Cl-photo assimilates. Export of both [¹³N] and [¹¹C]-Iabelledassimilates from the leaf and movement in the petiole in boththe light and the dark was inhibited by source leaf anoxia (i.e.nitrogen gas). Translocation was re-established at the samerate when the feed leaf was exposed to gas containing more than2% O₂ which permitted dark respiration to proceed. After aninitial feeding of either ¹¹CO₂ or [¹³N]-ammonia at ambient(21%) O₂ exposure of the source leaf to 2% O2, or 50% O² didnot alter the rates of translocation, indicating that changesin photosynthetic activity in the source leaf due to photorespiratoryactivity need not markedly alter, at least during the shortperiod, the loading and translocation of either [¹¹C ] or [¹³N]-labelledleaf products. Key words: Translocation, CO₂, NH₃, Leaves, Helianthus annuus, Lupinus albus     

Respiratory ETS activity of plankton in the northwestern Alboran Sea: seasonal variability and relationship with hydrological and biological features

Respiratory electron transport system (ETS) activity was measuredin plankton samples (<200 µm) collected in the NW AlboranSea. Sampling was carried out during seasonal cruises (summerand autumn 2003 and winter and spring 2004) in 12 stations locatedin transects off the coast of Malaga (southern Spain). Thiswork reports for the first time seasonal variations of the Arrheniusactivation energy (Ea) as well as being the first study to addressCO₂ balance in the NW Alboran Sea. These variations were relatedto changes in the phytoplankton community assemblage, whichcould ultimately be caused by the seasonal variability of hydrologicalconditions. ETS activity was significantly higher in summer,coinciding with a higher chlorophyll a (Chl a) concentrationand relatively high levels of particulate organic matter. TheETS:Chl a_total ratios were low during the four seasons, suggestinga high contribution of autotrophic phytoplankton to the respiratoryactivity of planktonic community. Respiratory CO₂ production(RCP) calculated from ETS activity ranged from 4.6 to 28.1 mgC m^–3 day^–1 during the four cruises. Chl a-specificRCP was lower than the maximum photosynthetic rates reportedin the literature for the studied area, suggesting that primaryproduction (PP) and respiration in the water column might beunbalanced.     

Effects of Water Stress on the Respiratory and Nitrogen-fixing Activity of Soybean Root Nodules

Seventy-five per cent of the N₂-fixing activity (measured asthe reduction of C₂H₂ to C₂H₄) and 50 per cent of the respiratoryactivity of detached soybean root nodules was lost when thewater potential () of the nodules was lowered from approximately–1 ? 105 Pa (turgid nodules) to –9 ? 105 Pa (moderatelystressed nodules). Severely stressed nodules ( = –1.8? 10⁶ Pa) showed almost total loss of N₂-fixing activity andup to 80 per cent loss of respiratory activity. Increasing theoxygen partial pressure (PO₂) from 10⁴ to 10⁵ Pa completelyrestored both N₂-fixation and respiration in moderately stressednodules, but only partial recovery was possible in severelystressed nodules. The activity of the stressed nodules was verylow at low PO₂ (5 ? 10³ and 10⁴ Pa). The C₂H₂-reducing activityof nodule slices, nodule breis, and bacteroids from turgid andmoderately stressed nodules was almost identical but some activitywas lost in the breis and bacteroids from severely stressednodules. Calculations showed that at low PO₂ (10⁴ and 2 ? 10⁴Pa), the rate of O₂ diffusion into severely stressed noduleswas ten times lower than that for turgid nodules, but only fourtimes lower at a higher PO₂ (4 ? 10⁴ Pa). Carbon monoxide inhibitionof C₂H₂ reduction was slower in stressed nodules than in turgidnodules. The results are discussed in view of the possible developmentof a physical barrier to gaseous diffusion and/or the possiblealtered affinity of the nodule leghaemoglobin for O₂ in thewater-stressed nodules.     

Differential modulation of voltage-dependent K+ currents in colonic smooth muscle by oxidants

The effect of oxidants on voltage-dependent K⁺ currents was examined in mouse colonic smooth muscle cells. Exposure to either chloramine-T (Ch-T), an agent known to oxidize both cysteine and methionine residues, or the colon-specific oxidant monochloramine (NH₂Cl) completely suppressed the transient outward K⁺ current (I_to) while simultaneously enhancing the sustained delayed rectifier K⁺ current (I_dr). In contrast, the cysteine-specific oxidants hydrogen peroxide (H₂O₂) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) exhibited partial and slow suppression of I_to by inducing a shift in channel availability of -18 mV without affecting I_dr. After enhancement by NH₂Cl or Ch-T, I_dr was sensitive to 10 mM tetraethylammonium but not to other K⁺ channel blockers, suggesting that it represented activation of the resting I_dr and not a separate K⁺ conductance. Extracellular dithiothreitol (DTT) partially reversed the effect of H₂O₂ and DTNB on I_to but not the actions of NH₂Cl and Ch-T on either I_dr or I_to. Dialysis of myocytes with GSH (5 mM) or DTT (5 mM) prevented suppression of I_to by H₂O₂ and DTNB but did not alter the effects of NH₂Cl or Ch-T on either I_dr or I_to. Ch-T and NH₂Cl completely blocked I_to generated by murine K_v4.1, 4.2, and 4.3 in Xenopus oocytes, an effect not reversible by intracellular DTT. In contrast, intracellular DTT reversed the effect of H₂O₂ and DTNB on the cloned channels. These results suggest that I_to is suppressed via modification of both methionine and cysteine residues, whereas enhancement of I_dr likely results from methionine oxidation alone. colon; colitis; redox; ion channel     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

Effects of Atmospheric O3 on Azolla-Anabaena Symbiosis

Cultures of water fern Azolla pinnata R. Br. exposed for 1 weekto either 30, 50 or 80 nl l^-1 O₃ showed significant reductionsin rates of growth and N₂ fixation, and had fewer heterocysts.Although the levels of glutamine synthetase (GS) and glutamatedehydrogenase (GDH) activity were decreased by low concentrationsof O₃ exposures (30 or 50 nl l^-1), significant increases inlevels of the same enzymes were caused by higher concentrationsof O₃ (80 nl l^-1). Increased levels of total protein, polyamines(putrescine and spermidine), and the xanthophyll-cycle precursorof abscisic acid (ABA), violaxanthin, were also found with higherlevels of O₃ (80 nl l^-1). Levels of ABA itself were significantlyincreased by low level O₃ fumigation (30 nl l^-1) but significantlydecreased by exposure to 80 nl l^-1 O₃. This may indicate thathigher levels of atmospheric O₃ inhibit the final stages ofABA biosynthesis from violaxanthin.Copyright 1994, 1999 AcademicPress Abscisic acid, nitrogen assimilation, nitrogen fixation, ozone pollution, polyamines, violaxanthin     

Effects of Preillumination on Dark Nitrogen Fixation and Respiration by Anabaena Cylindrica

In whole filaments of Anabaena cylindrica dark nitrogen-fixingactivity (measured as acetylene reduction) and respiration increasedwith the light intensity of a fixed period of preillumination,saturating at ca. 10,000 lux. With saturating light during preillumination,the amount and duration of dark nitrogen-fixing activity increasedwith length of preillumination, but respiration declined rapidlyin the dark. At dark respiration rates below 250 nmol O₂ uptake mg protein^–1?h^–1(State 1) no significant nitrogen-fixing activity is observed.From 250 to 550 nmol O₂ uptake?mg protein^–1?h^–1(State 2), nitrogen-fixing activity depends on O₂ uptake whileabove 550 nmol O₂ uptake?mg protein^–1?h^–1 (State3), nitrogen-fixing activity no longer increases with furtherincrease in O₂ uptake rate. (Received June 18, 1983; Accepted November 10, 1983)     

Regeneration of Ribulose 1,5-bisphosphate and Ribulose 1,5-bisphosphate carboxylase/oxygenase Activity Associated with Lack of Oxygen Inhibition of Photosynthesis at Low Temperature

The nature of the lack of oxygen inhibition of C₃-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO²), 21 kPa p(O₂), balance N₂) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O₂). At 20°C, lowering p(O₂) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O₂) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O₂). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O₂) suggestingthat RuBP regeneration was reduced at low p(O₂) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O₂) was 24% higherthan at 21 kPa p(O₂). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O₂). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase     

A comparative study on the effect of O2 on photosynthetic carbon metabolism by Chlorobium thiosulfatophilum and Chromatium vinosum

The reductive carboxylic acid cycle appears to be the majorcarbon assimilation pathway in green sulfur bacteria, Chlorobiumthiosulfatophilum. While cyanide was relatively ineffectivein inhibiting the bacterial photosynthetic CO₂ fixation, photosynthesiswas strongly impaired in an O₂-containing atmospheric environment.No glycolate formation was detected in Chlorobium under an O₂atmosphere. In the purple sulfur bacteria, Chromatium vinosum,however, photosynthesis was highly sensitive to cyanide, andin a short-term incubation (up to 10 min) photosynthetic CO₂fixation was found to be relatively indifferent to an O₂-containingatmosphere of up to 100% O₂. Significant formation of glycolatewas demonstrated upon a very brief exposure to O₂, whereas thetotal photosynthetic CO₂ fixation was slightly affected. However,ribulose-1,5-bisphosphate carboxylase activity in Chromatiumextract was competitively inhibited by O₂ in a similar mannerto the higher plant enzyme, K¹(O₂) value being 0.7 mM at pH8.2. The percentage of incorporation of ¹⁴CO₂ into glycolateand glycine under an O₂-containing atmosphere declined withincreasing levels of bicarbonate concentrations in the medium.The Warburg effect and biosynthetic mechanisms involving glycolatein photosynthetic bacteria are discussed. ¹ This is paper XXXIX in the series "Structure and Functionof Chloroplast Proteins". Paper XXXVIII is reference (6) Asamiand Akazawa (1977). This research was supported in part by grantsfrom the Ministry of Education of Japan (111912), the TorayScience Foundation (Tokyo), and the Japan Securities ScholarshipFoundation (Tokyo). (Received January 28, 1977; )     

Some Characteristics and Inhibitors of Indoleacetic Acid Oxidase from Tissue 2

Extracts from tissue cultures of crown-gall from Parthenocissuscatalysed the destruction of indoleacetic acid in vitro withoptimum activity at pH 4·5. The presence of two co-factors,Mn⁺⁺ and 2,4-dichlorophenol, was necessary for this activity,which was found to be strictly aerobic. Chlorogenic acid, caffeic acid, scopoletin, ferulic acid, andgibberellic acid markedly inhibited IAA-destruction. Chlorogenicacid inhibition was reversed by the addition of H₂O₂. Chlorogenicacid was not oxidized by the IAA-destroying system and did notbehave as a competitive inhibitor. The IAA-oxidase extract manifested peroxidase and phenolaseactivity with catechol and pyrogallol as substrates. However,this activity was greater at pH 7·0 than at the optimumfor IAA-oxidase activity, pH 4·5. Further evidence ofthe existence of these two enzymes in the intact tissue wasdemonstrated by histochemical studies. In tissue slices, peroxidaseactivity was very high and widely distributed while phenolaseactivity was low and restricted to localized centres of thetissue.