The Organic Acid Metabolism of Cox's Orange Pippin Apples: I. SOME EFFECTS OF THE ADDITION OF ORGANIC ACIDS TO THE PEEL OF THE FRUIT

1. The basic respirations (CO₂-output and O₂-uptake) of Cox'sOrangePippin apples and of the peel tissue prepared from themwerecompared in fruit in various stages of development, bothinitiallyand after storage at 12°C. Both show the samegeneral trend,although as the apples become mature the peakvalue of the respirationclimacteric tends to rise in the wholefruit and fall in thepeel.
2. The effect of adding malate orcitrate on the respiration ofthe same samples of peel was studied.
3. Three broad stages of development were observed. During thefirst stage (petal fall to 60 days after) the metabolic patternappears to be different from the two later stages. Here O₂-uptakeas well as C₂-output are influenced by the addition of bothmalate and, to a considerably less extent, citrate. In stage2 (60–125 days from petal fall), the malate effect (CO₂-output)is small until after detachment from the tree, when it risessharply. In stage 3 (125 days to full maturity) the malate effectfollows the course expected for earlier work, namely, it developsat the same time as the climacteric rise in respiration. Thepossible reasons for the different behaviour of the peel atthe three stages is discussed.
4. Results were similar in generaltrend for Cox's Orange Pippinapples grown on different rootstocksand under different culturalconditions.
5. It is suggested thatthe malate effect is most active in theepidermal and hypodermaltissues of the fruit.

     

Coupling of malate decarboxylation to CO2 fixation and the reduction of 3-phosphoglyceric acid in corn bundle sheath cells,2

1. In the presence of NADP⁺ and Mg⁺⁺, the bundle sheath strandsisolated from corn (Zea mays) leaves by cellulase treatmentsdecarboxylated malate in the light at an initial rate (200 µmoles/mgchl.hr), which was sufficient to account for photosyntheticCO₂ fixation in intact leaves. This rate gradually slowed downand then stopped. The final level of the malate decarboxylatedwas approximately equal to the amount of NADP⁺ added.
2. Rapidand continued decarboxylation of malate was observed whenNADP⁺,3-phosphoglyceric acid and ATP (and Mg⁺⁺) were addedtogether.The addition of ADP instead of ATP showed a similareffect.Light did not show any effect on the malate decarboxylationin the presence of ATP or ADP.
3. When malate was added to thebundle sheath strands in the presenceof exogenous NADP⁺ NADP⁺was rapidly reduced. The reductionstopped after 2 min when,73% of the added NADP⁺ was reduced.The further addition of3-phosphoglyceric acid and ATP broughtabout a decrease in theNADPH-level, which rose again to attaina new steady level.
4. The transfer of radioactivity from (1-¹⁴C-3-phosphoglycericacid to dihydroxyacetone phosphate in the bundle sheath strandsin the presence of ATP and NADP⁺ was greatly enhanced by theaddition of malate.
5. In the presence of ribose 5-phosphateand ATP, the rate of ¹⁴C-transferfrom (4-¹⁴C)-malate to theintermediates of the reductive pentosephosphate cycle was equalto that of ¹⁴CO₂ fixation in the light.

All these results support the current view that in the bundlesheath cells of C₄ plants belonging to the NADP-malic enzyme-group,the decarboxylation of malate is coupled to the fixation ofthe released CO₂ and the reduction of 3-phosphoglyceric acidformed as a result of CO₂ fixation. ¹ Part of this research was reported at the 40th Annual Meetingof the Botanical Society of Japan Osaka, December, 1975. ³ Present address: Laboratory of Chemistry, Faculty of Medicine,Teikyo University, 359 Otsuka, Hachioji-City, Tokyo 173, Japan. (Received April 30, 1977; )     

DIFEKTITA AUTOTROFO DE MUTACIITA CHLAMYDOMONAS1

A mutant of Chlamydomonas moewusii is described which, thoughcapable of CO₂-fixation and O₂-evolution in light, was unableto grow at appreciable rates in the absence of an organic substrate.Growth of the mutant approached that of the wild type in citratemedia; fumarate, succinate or malate stimulated growth lesseffectively. (Received August 8, 1960; )     

The Inhibition of the Activity of Apple Mitochondria by Oxaloacetate

The inhibitory effect of oxaloacetate (OAA) on the activityof mitochondria isolated from the peel of Cox's Orange Pippinapples has been investigated. A given concentration of OAA causesa longer inhibition of succinate than of malate oxidation andthe rate of disappearance of OAA is faster in the presence ofmalate than in that of succinate. Mg⁺⁺⁺, Al⁺⁺⁺, ATP, and glutamateaccelerate the disappearance of inhibition by OAA; Ca⁺⁺ reinforcesthe inhibition. It is established, by estimation of the oxoacids in the reaction mixtures, that the relief from inhibitionis directly due to removal of OAA. The fall in rate of O₂ uptakewith time, using succinate or malate as substrate, is accompaniedby an accumulation of OAA, and the inhibition of succinate oxidationby malate is due to the increased OAA production when malateis oxidized. Some OAA is broken down non-enzymically to formpyruvate and the rate of breakdown is enhanced by Mg⁺⁺; someis metabolized via the Krebs cycle; some disappear in a coupledreaction between pyruvic and malic dehydrogenases to form citrateand malate, and some can be removed by transamination. It issuggested that all these may be factors in a regulatory actionof OAA on the operation of the Krebs cycle. It is relevant inthis connexion that very small amounts of OAA inhibit the activityof the Krebs cycle when they are produced at the active siteswithin the mitochondrion.     

Metabolic Changes in Excised Fruit Tissue. IV. Changes Occurring in Discs of Apple Peel During the Development of the Respiration Climacteric

It is shown that a sequential development of a series of enzyme systems occurs in the peel of the apple as the respiration climacteric develops in the whole fruit. The sequence of development of these systems, i.e. acetate incorporation into lipid, production of ethylene, incorporation of amino acid into protein and, finally, the decarboxylation of added malate (malate effect) is the same as that shown earlier for the short term (24 hr) aging of peel discs from pre-climacteric apples. As these systems appear in the initial discs from fruit passing through the climacteric they gradually cease to increase during the 24 hour aging period. Uptake studies show that none of the changes in these systems can be due solely to changes in the permeability of the tissue over the climacteric period. On the basis of these results it is tentatively suggested that the aging of discs from pre-climacteric tissue might provide a model system for a detailed study of the physiological and biochemical changes occurring during the climacteric of apple fruits.     

Diurnal changes in malate-decarboxylation activity in the leaves of a CAM plant, Bryophyllum daigremontianum

Bryophyllum diagremontianum plants grown under light-dark regimeswere exposed to one more cycle of the regime or to continuousdarkness for 24 hr. Photosynthetic O₂ evolution by leaf segmentsfrom these plants was investigated in the presence of 15 mMNaHCO₃ (CO₂-dependent O₂ evolution) or in the absence of CO₂(malate-dependent O₂ evolution). The malate-dependent O₂ evolutionserved as an index of the activity of malate decarboxylation.Malate content was respectively 67, 64 and 85 µmoles/g.fwin leaves measured at 7 hr 30 min in light and 6 hr 26 min inthe dark from plants under the light-dark regime (light 12 hr/dark12 hr) and those measured at 6 hr 26 min in the dark from plantsunder the continuous dark regime. The malate- and CO₂-dependentphotosynthetic O₂ evolutions in the same leaves were 9.7 and22, 0.2 and 17, and 16 and 26 µmoles/g.fw.hr, respectively.Thus, the diurnal change in capacity for malate-dependent O₂evolution was relieved by continuous dark treatment. These results suggest that the diurnal change in malate decarboxylationin this crassulacean acid metabolism plant does not occur byan endogenous rhythm. This further indicates lack of an endogenousrhythm for the influx-efflux of malate across the vacuole andin malate decarboxylation enzyme activity. (Received August 1, 1979; )     

Activation of Glyoxylate Cycle Enzymes in Cucumber Fruits Exposed to CO2

Cucumber fruits exposed to a 60% CO₂ environment for 3 d at20°C showed a higher respiration rate, a lower respiratoryquotient, and lower levels of malate, citrate + isocitrate,and glyoxylate than did control fruits. Moreover, in the CO₂treatment, fumarate and succinate increased dramatically onthe first day and after the second day, respectively, while2-oxoglutarate showed a temporary increase on the first dayand a subsequent decrease. Isocitrate lyase and malate synthaseactivity tended to increase throughout the experimental periodof the CO₂ treatment. These results appear to point to a rapidoperation of glyoxylate cycle due to high CO₂. (Received November 14, 1997; Accepted March 2, 1998)     

PARTIAL PHOTO-REPRESSION OF THE GLYOXYLATE BY-PASS IN EUGLENA

1. Addition of exogenous acetate or ethanol to autotrophic culturesof Euglena gracilis strain Z induces formation of the glyoxylateby-pass.
2. Visible light decreases the activity of malate synthasein greenEuglena by about 50%. No such effect was found in apermanentlybleached mutant.
3. Aconitase activity parallelsthat of malate synthase, but isocitricdehydrogenase activityis constant under all conditions examined.
4. Oxygen consumptionis proportional to the activities of malatesynthase and aconitase,but not to that of isocitric dehydrogenase.
5. The results ofsimilar studies with other growth substrates(pyruvate, malate,succinate) suggest that some of the oxygenconsumed by C₂-grownEuglena may not be associated with energyproduction.

(Received March 25, 1966; )     

Oxygen enhancement of photosynthesis in Anacystis nidulans cells1

Oxygen enhanced photosynthetic ¹⁴CO₂ fixation in Anacystis nidulanscells. Results obtained under different conditions revealedthe following properties of the oxygen enhancement:

1. The enhancement was most significant at ca. 10% O₂. Furtherincrease in oxygen concentration decreased the enhancing effect.The rate under 100% O₂ was equivalent to or a little higherthan that under N₂ gas.
2. b) With the increase in CO₂ concentration,the magnitude ofthe enhancing effect decreased. No oxygen enhancementwas observedwhen the CO₂ concentration. was raised to 9,000ppm.
3. c) The enhancement was observed only at high light intensities.No enhancement was observed when the rate of photosynthesiswas limited by light intensity.
4. Ribulose 1,5-diphosphate (RuDP)carboxylase activity was demonstratedin the extract obtainedfrom A. nidulans cells. We also foundthat the RuDP carboxylaseactivity in this extract was competitivelyinhibited by oxygen.
5. Based on the above-mentioned results, the possible mechanismunderlying the observed enhancing effect of oxygen was discussed.

(Received May 10, 1976; )     

The Metabolism of Acetaldehyde by Plant Tissues

Apples and oranges can absorb appreciable amounts of acetaldehydevapour, but acetaldehyde does not accumulate in the tissues,in the presence or absence of oxygen. When the fruit is givenacetaldehyde the loss of carbon as CO₂ + ethanol equals thatlost from carbohydrate + acid+acetaldehyde. Part of the addedacetaldehyde is reduced to ethanol by NADH₂ and the rate ofglycolysis is increased; the remainder is oxidized to CO₂. Respiration of apples is limited by oxygen; the output of CO₂is only slightly increased at the beginning of the treatmentwith acetaldehyde, but afterwards it declines; acetaldehydespares oxidation of carbohydrate. In oranges, availability of substrate limits respiration, andacetaldehyde stimulates CO₂-production and O₂-uptake. In theabsence of oxygen, acetaldehyde is reduced to ethanol, and thequotient CO₂/ethanol falls.     

Formation of Hydrogen Peroxide and Oxygen Dependence of Photosynthetic CO2 Assimilation by Intact Chloroplasts

1. Hydrogen peroxide excretion by photosynthesizing intact spinachchloroplasts was determined. The rates were dependent on theoxygen concentration and on the ATP/NADPH requirement of thefinal electron acceptor. Upon CO₂ assimilation a maximum rateof 0.9 µmol H₂O₂/mg chlorophyll/hr and half saturationat 7.5 x 10^–5 M O₂ were found. Excretion of H₂O₂ was considerablyreduced upon photosynthetic reduction of glycerate 3-phosphateor oxaloacetate.
2. Light- and HCO₃-saturated CO₂ assimilationwas inhibited bymore than 50% by anaerobic conditions, whereuponquantum efficiencywas also drastically decreased. However,no anoxic influencewas detected with glycerate 3-phosphateas the terminal electronacceptor and the quantum requirementwith this acceptor wasnot increased by anaerobiosis. Thus theenhancing effect ofoxygen on CO₂ assimilation was ascribedto an improvement ofphotosynthetic ATP supply.
3. Since thestimulation of anaerobic photosynthetic CO₂ assimilationbyoxygen was markedly greater than the concomitant increaseinH₂O₂ evolution, photosynthetic oxygen reduction alone isnotsufficient to produce the required additional ATP for theobservedenhanced CO₂ assimilation. But it provides a meansto avoidthe over-reduction of photosynthetic electron carriersand thusenables aerobic cyclic photophosphorylation. This supportsthehypothesis that cyclic photophosphorylation is not an alternativeto ATP formation by "pseudocyclic" electron transport, but ratherthat it depends on the latter.

(Received January 5, 1981; Accepted March 9, 1981)     

LIGHT-INDUCED REDUCTION OF NITRATE, NITRITE AND HYDROXYLAMINE IN A BLUE-GREEN ALGA, ANABAENA CYLINDRICA

1. Reduction of nitrate, nitrite and hydroxylamine by intact cellsof Anabaena cylindrica was investigated with special referenceto the stimulating effect of light on these processes.
2. Itwas found that in light and under anaerobic condition thesecompounds are reduced to ammonia, with the production of extraoxygen. The stoichiometry of the reactions under these conditionscan be represented as follows: HNO₂+H₂O=NH₂+2O₂ HNO₂+H₂O=NH₂+1O₂ NH₂OH+H₂O=NH₂+O₂+H₂O
3. Reduction of nitrite and hydroxylaminewas markedly suppressedby CMU in the light but not in the dark.KCN inhibited reductionto the same extent both in the lightand in the dark. Reductionin the light was much less sensitiveto the uncoupling agent,DNP, than was that in the dark.
4. Atlow light intensities, CO_2– was suppressed by 20–30per cent by the simultaneous provision of nitrite, but the nitritereduction was not affected at all by CO₂. At high light intensities,reduction of nitrate and nitrite was considerably acceleratedby CO₂
5. On the basis of these findings, a possible mechanismfor thelight stimulation of the reactions in question was brieflydiscussed.

(Received August 22, 1962; )     

Apparatus for the Measurement of Gaseous Conditions inside an Apple Fruit

1. Two forms of apparatus are described, one for the routine analysisof the internal atmosphere of an apple fruit and another forthe measurement of (i) carbon dioxide output, (ii) internalgas concentrations, (iii) atmospheric pressure within the fruit,(iv) permeability of the fruit to gases.
2. The use of thesetwo apparatuses to follow changes within thefruit as a resultof the application of a skin-coating is describedand the resultsobtained are discussed.
3. It is shown that the fall in pressurewhich occurs as a resultof the cooling of the fruit due toevaporation of the appliedcoating can only form a small fractionof the total fall inpressure observed as a result of the applicationof the coating.
4. It is shown that coating the fruit with anoil-water emulsioncauses a deficit in the combined concentrationof CO₂ and O₂within the fruit below the 21 per cent, observedin similaruncoated fruit.
5. An explanation of this phenomenonis advanced, and it is suggestedthat the modification of theinternal atmosphere brought aboutby the skin-coating, if itcan be suitably controlled, willprove valuable in increasingthe cold-storage life of apples.

The work described in this paper was carried out as part ofthe programme of the Food Investigation Organization of theDepartment of Scientific and Industrial Research.     

Photosynthetic and light-enhanced dark fixation of 14CO2 from the ambient atmosphere and 14C-bicarbonate infiltrated through vascular bundles in maize leaves

1. The capacity of light-enhanced dark fixation of ¹⁴CO₂ from theambient atmosphere decayed following time-course characteristicsof a first-order reaction (half-life, 1–2 min). The levelof phosphoenolpyruvate in maize leaves under CO₂-free air didnot decrease in the dark subsequent to preillumination. Theseresults indicate that phosphoenolpyruvate carboxylase is activatedin light and quickly inactivated in the following darkness.
2. Removal of oxygen from the atmosphere did not exert any effecton the products of light-enhanced dark fixation of ¹⁴CO₂ providedfrom the atmosphere, the major labeled compounds being malateand aspartate. This confirms that the transfer of carboxyl carbonof C₄-acids to form 3-phosphoglycerate is light-dependent.
3. WhenNaH¹⁴CO₃ solution was vacuum-infiltrated through vasculartissuesof maize leaves, the main initial photosynthetic ¹⁴CO₂fixationproducts were phosphate esters. This indicates thatby thistechnique, ¹⁴CO₂ could be directly provided to the bundlesheathcells, and was fixed via the reductive pentose phosphatecycle.On the other hand, the main initial ¹⁴CO₂-fixation productswere malate and aspartate even when ¹⁴CO₂ was provided throughvascular tissues in the dark immediately following preillumination.The possible regulatory mechanisms underlying the above findingsare discussed.

¹ This work was reported at the 4th International Congress onPhotosynthesis, Reading, September 1977. Request for reprintsshould be addressed to S. Miyachi, Institute of Applied Microbiology,University of Tokyo, Bunkyo-ku, Tokyo 113, Japan ² Present address: Okinawa Branch of Tropical Agriculture ResearchCenter, Ishigaki-shi, Okinawa 907, Japan. (Received October 28, 1977; )     

Carrier-mediated transport of metabolites in purified bean mitochondria

1. The mechanism of transport of Krebs cycle intermediates, phosphateand sulfurcontaining compounds across the membrane of purifiedbean mitochondria was investigated by directly measuring dieexchange between intramitochondrial labelled substrates andexternal anions and by testing die inhibitor sensitivity ofdiese transport processes.
2. The exchange between intramitochondrialphosphate and externalphosphate or sulfite is insensitive toN-ediylmaleimide or butylmalonatewhen either is added alone,but is completely inhibited by N-ethylmaleimideplus butylmalonateor by mersalyl. Internal phosphate is exchangedwith malate,succinate, oxaloacetate, sulfate and thiosulfate;these reactionsare inhibited by butylmalonate but not affectedby N-ethylmaleimide.
3. Internal sulfate is exchanged with malate, malonate, succinate,phosphate and sulfite in a butylmalonate- and mersalyl-sensitivereaction. Also the exchanges of malonate with phosphate, sulfateand sulfite are inhibited by butylmalonate and mersalyl. Onthe other hand, the exchange between intra- and extramitochondrialmalonate is completely inhibited only by the combination ofbutylmalonate and 1,2,3-benzenetricarboxylate.
4. Citrate isexchanged with some di- and tricarboxylates and phosphoenolpyruvate(but not with phosphate, sulfate, oxoglutarate, trans-aconitateand benzenetricarboxylates). These exchanges are inhibited by1,2,3-benzenetricarboxylate, but not by 1,2,4-benzenetricarboxylateor 1,3,5-pentanetricarboxylate.
5. Oxoglutarate is exchangedwith succinate, malate, malonate andoxaloacetate (but not withphosphate, citrate or phosphoenolpyruvate)in a mersalyl-insensitive,butylmalonate- and phenylsuccinate-sensitivereaction.
6. Weconcluded that bean mitochondria contain the following transportsystems: a phosphate carrier inhibited by N-ethylmaleimide ormersalyl, a dicarboxylate carrier inhibited by butylmalonateor mersalyl, a citrate carrier inhibited by 1,2,3-benzenetricarboxylateand an oxoglutarate carrier inhibited by phenylsuccinate orbutylmalonate but insensitive to mersalyl.

(Received June 23, 1976; )     

Effects of carbon dioxide on activity of apple mitochondria

Effects of CO₂ on mitochondrial activity of apple (Malus pumila Mill. var. Richared Delicious) were studied in two ways. Immediate effects were determined by imposing 3 to 18% CO₂-bicarbonate mixtures on isolated apple mitochondria, and long term effects were determined by extracting mitochondria from apples that had been stored for intervals in atmospheres containing 6 or 12% CO₂ plus 3% O₂. The CO₂-bicarbonate systems had immediate and broad effects on mitochondrial oxidations: 18% CO₂ stimulated malate oxidation about 10%; suppressed α-ketoglutarate, citrate, and NADH oxidations about 10%; and suppressed fumarate, pyruvate, and succinate oxidations about 32%. The effects of lower CO₂ concentrations varied with substrates. Mitochondria isolated from fruit stored in 6 or 12% CO₂ possessed a reduced capacity to oxidize added succinate or NADH, but retained a marked sensitivity to CO₂-bicarbonate mixtures. Respiratory control in these mitochondria was somewhat reduced, but CO₂ had not acted as a strong uncoupling agent.     

Endogenous light-on rhythm in respiration of a long-day duckweed, Lemna gibba G3 II. On basic and rhythmic components of the rhythm

Effects of respiratory substrates (glucose, malate, citrateand pyruvate) and inhibitors (fluoride, iodoacetate, azide andDNP) on the O₂-uptake rhythm in a long-day duckweed,Lemna gibbaG3 in continuous light period were examined. Rates of O₂-uptake at the starting point (6 hr after the beginningof a continuous light period) and at the time of the first peakof the rhythm (18 hr after the beginning of a continuous lightperiod) were equally increased by exogenous substrates. Sensitivityof respiration to fluoride or iodoacetate was almost the sameat the 6th and 18th hr. The O₂-uptake (at the 6th, 18th, 30thand 42nd hr) was increased by DNP by the same amount. Azideat lower concentrations than 5X10^–4 M did not affect O₂-uptakeat the 6th hr, but inhibited uptake at the 18th hr. In the presenceof 5 X 10^–4 M of azide the rates of O₂-uptake at the 18th,30th or 42nd hr were down to the rate at the 6th hr, which wasinsensitive to azide. These results suggest that the O₂-uptakerhythm consists of two components, i.e. the basic respirationwhich is promoted by exogenous substrate, sensitive to DNP andinsensitive to azide; and rhythmic respiration, which is sensitiveto azide, but is not influenced by exogenous substrate and DNP. (Received February 19, 1971; )     

The Effect of Subjecting Peas to Air Enriched with Carbon Dioxide: II. RESPIRATION AND THE METABOLISM OF THE MAJOR ACIDS

Whole peas at about 75 per cent of their maximum fresh weightwere subjected to 5–30 per cent CO₂ in air for periodsof from 1–6 d, then returned to air for a further 1 d.Samples were withdrawn at intervals and organic acids, ^TCO₂and ethanol estimated as well as the rate of respiration. Slicesof cotyledons suspended in water were also subjected to highconcentrations of CO₂ in air for 3 h. The rate of respiration was inhibited progressively by increasein CO₂ content of the tissue. The high internal CO₂ contentof the intact pea causes an inhibition of its rate of respirationby about 25 per cent. Alcohol production commenced at between10 and 15 per cent CO₂ in the ambient gas and slowly increasedin rate up to 37 per cent. The CO₂-air mixtures reduced the content of malate, pyruvateand -oxoglutarate, increased that of succinate and left citrateunaffected. On return to air malate rose rapidly and succinatefell slowly to their original concentrations. During the sameperiod the concentration of PEP fell sharply and after about1 h rose again, whereas oxalacetate showed a reverse response.It is argued that the rapid re-synthesis of malate was by carboxylationof PEP to oxalacetate and that this reaction was stimulatedby a change in pH rather than by the direct effect of the changein concentration of CO₂. In one experiment ¹⁴CO₂ was supplied for 2 h before return toair and the movement of ¹⁴C followed for 6 h. The results supportthe method of re-synthesis of malate proposed.     

Effect of inhibitors on ammonia-, 2-oxoglutarate-, and oxaloacetate-dependent o(2) evolution in illuminated chloroplasts

The evolution of O₂ in spinach chloroplasts in the presence of oxaloacetate (OAA) was inhibited by a wide range of dicarboxylates. In contrast, (ammonia, 2-oxoglutarate)-dependent O₂ evolution was stimulated by malate, succinate, fumarate, glutarate, maleiate, and l-tartrate although OAA has little effect. This increase in O₂ evolution was accompanied by a similar increase in ¹⁴C incorporation from [5-¹⁴C]oxoglutarate into amino acids which was sensitive to azaserine inhibition. Glutamate and aspartate inhibited (ammonia, 2-oxoglutarate)-dependent O₂ evolution, but this inhibition was relieved by the addition of succinate, malate, or fumarate. OAA-dependent O₂ evolution also was inhibited by glutamate and aspartate, but succinate, malate, or fumarate had little effect on this inhibition. Phthalonate and n-butyl malonate inhibited (ammonia, 2-oxoglutarate)-dependent O₂ evolution competitively with respect to 2-oxoglutarate and uncompetitively with respect to malate. Both these inhibitors inhibited OAA-dependent O₂ evolution competitively. This evidence suggests that different mechanisms might be involved in the transport of OAA, 2-oxoglutarate, and malate into the chloroplasts.     

RNA synthesis during morphogenesis of the fungusMucor racemosus

Bacteroides succinogenes produces acetate and succinate as major products of carbohydrate fermentation. An investigation of the enzymes involved indicated that pyruvate is oxidized by a flavin-dependent pyruvate cleavage enzyme to acetyl-CoA and CO₂. Active CO₂ exchange is associated with the pyruvate oxidation system. Reduction of flavin nucleotides is CoASH-dependent and does not require ferredoxin. Acetyl-CoA is further metabolized via acetyl phosphate to acetate and ATP. Reduced flavin nucleotide is used to reduce fumarate to succinate by a particulate flavin-specific fumarate reductase reaction which may involve cytochrome b. Phosphoenolpyruvate (PEP) is carboxylated to oxalacetate by a GDP-specific PEP carboxykinase. Oxalacetate, in turn, is converted to malate by a pyridine nucleotide-dependent malate dehydrogenase. The organism has a NAD-dependent glyceraldehyde-3-phosphate dehydrogenase. The data suggest that reduced pyridine nucleotides generated during glycolysis are oxidized in malate formation and that the electrons generated during pyruvate oxidation are used to reduce fumarate to succinate.