Glucose 6-phosphate dehydrogenase from sweet potato: Effect of various ions and their ionic strength on enzyme activity

Activity of glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate:NADP oxidoreductase, EC 1.1.1.49 [EC] ) preparation from sweet potatoroot tissue was markedly altered in the presence of variousions. Cations or anions were effective in the following order:Na^$, K^$>Tris^$>NH₄^$>Mg^2$>Ca^2$, or Cl^–>NO₃^–,HPO₄^2–>SO₄^2–>HCO₃^–. Activity was inhibitedat high concentrations of Ca^2$, and HCO₃^–,. In an investigationon the dependence of the activity on pH, two activity peakswere clearly observed at low ionic strength. Ionic strength altered both the Km and Vmax for glucose 6-phosphate(G6P). A Lineweaver-Burk plot for the enzyme, with respect toG6P, showed a bimodal nature at low ionic strength; suggestingnegative cooperativity. Deviation from linearity of the plotwas less with an increase in the ionic strength. ¹ Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku, Tokyo 113. (Received September 18, 1971; )     

Relationship between light-induced potential change and internal ATP concentration in tonoplast-free Chara cells

The effect of the intracellular concentration of ATP ([ATP]₁)on the light-induced potential change (LPC) in tonoplast-freeChara cells was studied. The LPC was hardly affected by loweringthe [ATP]₁ by about 1/10 or by raising it to about 10 timesthe normal cytoplasmic concentration (0.5–1.3 mM). Theinsensitivity of LPC to [ATP]₁ excludes the possibility thatan increase in [ATP]₁ due to photosynthesis may induce the LPC.However, extreme lowering of the [ATP]₁ to about 1–2 µMcompletely inhibited LPC, although photosynthetic O₂ evolutionwas not significantly inhibited. This fact supports the hypothesisthat light stimulates the putative H⁺pump fueled by ATP. Theuncoupling agents DNP and CCCP greatly depolarized the membrane,and inhibited LPC strongly, but they did not decrease [ATP]₁.Photosynthetic O₂ evolution was inhibited to some extent by2 µM CCCP and strongly inhibited by 0.1 mM DNP. Sincethe membrane resistance increased significantly, these chemicalsare believed to act on the membrane as an inhibitor of the electrogenicH⁺ pump not as an H⁺conductor. Introduction of 1 mM ATP intocells treated with uncouplers, to a large extent restored theirability to produce LPC although the membrane potential in darknesswas maintained at a low level. ¹Present address: Niigata College of Pharmacy, 5829 Kamishinei-cho,Niigata 950-21, Japan. ²Present address: Department of Agricultural Chemistry, Collegeof Agriculture, Kyoto University, Kyoto 606, Japan. ³Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan. (Received March 9, 1979; )     

Estimation of Cytoplasmic Free Mg2+ Levels and Phosphorylation Potentials in Mung Bean Root Tips by In Vivo 31P NMR Spectroscopy

The cytoplasmic [MgATP]/[ATP]_free ratios, free Mg²⁺ concentrations,and phosphorylation potentials in mung bean [Vigna mungo (L.)Hepper] root tip cells were investigated by ³¹P nuclear magneticresonance spectroscopy. ³¹P NMR spectra show well defined peaksdue to G6P, cytoplasmic P_i, vacuolar P_i, ATP, UDP-glucose andnicotinamide adenine nucleotides. The concentrations of phosphorusmetabolites were determined from quantitative ³¹P NMR spectra.The [MgATP]/[ATP]_free ratio was 9.45. Accordingly, about 90%of the cytoplasmic ATP was complexed to Mg²⁺. Utilizing thedissociation constant (K_d) determined for MgATP, the cytoplasmicfree Mg²⁺ concentration was estimated to be 0.4mM. The NMR-derivedphosphorylation potential, [ATP]/([ADP][P_i]), was 960 M^-1. Thesodium azide treatment decreased the [ATP]/[ADP] ratio and thephosphorylation potential, and increased the [Mg²⁺]^free. Metabolicinhibition may have been enhanced by an increase in [Mg^2+freeand a decrease in the free energy change for ATP hydrolysis,which resulted due to a decrease in the ATP level. ¹Present address: National Food Research Institute, TsukubaCity, Ibaraki 305, Japan. (Received February 8, 1988; Accepted June 1, 1988)     

Fatty acid synthesis by spinach chloroplasts I. Property of fatty acid synthesis from acetate

Intact chloroplasts (about 70% Class I chloroplasts) isolatedfrom spinach leaves incorporated 150 nmoles of [1-¹⁴C] acetateinto fatty acids per mg chlorophyll in 1 hr at pH 8.3, 25°Cand 25,000 lux. On electron and phase-contrast microscopiescombined with hypotonic treatment of chloroplasts, this syntheticactivity was shown to be proportional to the percentage of ClassI chloroplasts in the preparation. Light was necessary for thesynthesis, the activity in the complete reaction mixture inthe dark being only 2% of that in the light. The synthetic activityincreased with increasing intensities of light to reach saturationat 6,000 lux. CoA and ATP were most effective as cofactors,HCO₃^–, HPO₄^2–, Mg^2$ and Mn^2$ were less effective.ATP could be replaced by ADP in the presence of Pi, suggestingpossible supply of ATP by photophosphorylation. Omission ofthe NADPH-generation system and NADH did not affect the synthesis,indicating sufficient provision of endogenous NADPH and NADHin intact chloroplasts under light. Addition of DTE did notcause recovery of the synthetic activity of intact chloroplastsin the dark. ¹ Present address: Radioisotope Centre, University of Tokyo,Yayoi, Bunkyo, Tokyo 113, Japan. (Received August 26, 1974; )     

Changes in nicotinamide nucleotide content and glucose metabolism in wheat embryos during vernalization

Contents of nicotinamide nucleotides, NAD, NADP, NADH₂ and NADPH₂,in wheat embryos were determined during normal germination andcold treatment. They increased markedly in the early stage ofgermination then decreased later. During cold treatment, thesenucleotides increased initially as in normal germination, butdid not decrease in the later stages. The C₆/C₁ ratios during germination decreased gradually withaging, but after about the fourth day increased. This suggeststhat the pentose phosphate pathway operates actively. Duringcold treatment, the C₆/C₁ ratio decreased slightly with aging.This suggests that the EMP pathway operates predominantly inthe glucose metabolism. Based on these results, the correlationbetween NADPH₂ and glucose metabolism during cold treatmentwas discussed. Embryos which had absorbed labelled glucose were fractionatedinto several chemical components. The radioisotope accumulatedmainly in the sugar fraction, with small amounts in the organicacid, amino acid and nucleic acid fractions. Changes in thecontent of each component showed that sugar, organic acid andamino acid increased during cold treatment. ¹ Present address: Department of Biochemistry, Faculty of PharmaceuticalScience, Higashi Nippon Gaguen University, Ishikari-Tobetsu,Hokkaido 061-02, Japan. ² Present address: Hokkaido Forest Products Research Institute,Asahikawa 070, Japan. ³ Present address: Kakuto 534, Komae City, Tokyo 182, Japan. (Received November 1, 1976; )     

Kinetic Characterization of Two Phosphate Uptake Systems with Different Affinities in Suspension-Cultured Catharanthus roseus Protoplasts

We studied the kinetics of inorganic phosphate (P₁) uptake from0.1–1,000 µM P₁ by protoplasts from suspension-culturedcells of Catharanthus roseus (L.) G. Don. Concentration dependenceof [³²P]P₁ uptake revealed two kinetically different uptakesystems, a high-affinity system and a low-affinity system, withK_m values of 3.0 and 47 µM, respectively. Protoplastsfrom cells grown in P_i-rich media had a medium level of thelow-affinity activity and a very low level of the high-affinityactivity. It appeared low-affinity system is expressed constitutively,while the high-affinity system is regulated by the availabilityof P_i. When cells grown in a P_i-rich media were transferredto P_i-depleted media, the high-affinity activity increased significantlyafter 2 d, but the low-affinity activity was barely changed.Upon addition of 10 mM P_i, the high level of the high-affinityactivity fell to almost undetectable level in 1d. Both uptakesystems exhibited maximum activity between pH 5 and 6. ¹ Present address: Tokyo Research Laboratories, Kyowa HakkoKogyo Co., Ltd., 3-6-6 Asahi-cho, Machida, Tokyo, 194 Japan.     

Effect of NADP$ and glucose 6-phosphate on the sedimentation behavior of glucose 6-phosphate dehydrogenase from sweet potato

Sedimentation behavior of sweet potato glucose 6-phosphate dehydrogenasewas studied using the sucrose density gradient centrifugation.The relative s value to s_20, value of alcohol dehydrogenasewas determined to be about 6 in the absence of both NADP^$ andglucose 6-phosphate. In the presence of NADP^$, the enzyme wassedimented with a relative s value of about 9. The additionof glucose 6-phosphate did not affect the sedimentation behavior.When glucose 6-phosphate was added to the gradient medium containingNDAP^$, the enzyme was sedimented with a relative s value ofabout 6 or 7, depending on the concentration of glucose 6-phosphate. ¹ Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku. Tokyo, Japan. (Received February 13, 1971; )     

Light-induced changes in membrane potential in Spirogyra

Spirogyra cells exhibited changes in membrane potential whenthey were exposed to light. Cells made chloroplast-free didnot show any light-induced potential change (LPC) upon illuminationwith white light and also monochromatic red (680 nm) and farred (720 nm) light. LPC was observed when the cell containedonly a small fragment of chloroplast, whether the cell had anucleus or not. The magnitude of LPC depended on the amountof chloroplast in the cell. DCMU at 10^–5 M, CCCP at 10^–5 M and DNP at 10^–4M at pH 5.5 suppressed LPC, while CCCP at 1–5 ? 10^–6M, NH₄Cl at 5 ? 10^–2 M and DNP at 10^–4 M at pH 7.0stimulated LPC. PMS at 10^–4 M stimulated LPC and couldinduce LPC which was completely inhibited by DCMU. These factssuggest that LPC is related to noncyclic and cyclic electronflows. The influences of light and dark conditions and various metabolicinhibitors (DCMU, DNP, CCCP, NH₄Cl) on ATP level have been investigated.No significant difference in the ATP level was observed betweencells in the light and dark. DNP at 10^–4 M (pH 5.5) andCCCP at 5 ? 10^–6 M decreased the ATP level significantly,while DCMU and NH₄Cl only slightly. Good correlation was notfound between the total ATP level and LPC in Spirogyra. LPC occurred even when the external medium contained only asingle salt such as KCl, NaCl or CaSO₄. LPC was also recorded in chloroplasts in situ and in vitro.The mode of LPC of chloroplasts was quite different from thatof the cell. On illumination, the chloroplast potential changedvery rapidly and transiently in the positive direction thenrecovered spontaneously to almost the original potential level. Possible causes of LPC are discussed in relation to the electrogenicion pump. ¹ Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. (Received November 9, 1977; )     

Photosynthetic metabolism of 14CO2 in the process of the "glucose-bleaching" of Chlorella protothecoides

Changes in photosynthetic carbon metabolism during the glucosebleaching of Chlorella protothecoides cells were investigatedusing NaH¹⁴CO₃ as tracer. Several hours after incubating thegreen algal cells in the glucose medium in the dark, the ratesof ¹⁴C-incorporation into glucose polymers and sucrose decreasedand the incorporation into the lipid fraction (fatty acids)greatly increased. At this stage, the rate of photosynthetic¹⁴CO₂ fixation and the chlorophyll content were practicallythe same as in the starting green cells. Afterwards, the photosyntheticcapacity and chlorophyll content continued to decrease throughoutthe experimental period. In contrast, when photosynthetic ¹⁴CO₂fixation of green cells was carried out in the medium containingglucose, the rate of ¹⁴C-incorporation into glucose polymersincreased, though there was no change in the incorporationsinto sucrose and the lipid fraction. ¹Part of this investigation was reported at the Conference "ComparativeBiochemistry and Biophysics of Photosynthesis" (Japan-U.S. CooperativeScience Program) held at Hakone, Japan in 1967. ²Present address: Faculty of Agriculture, Tamagawa University,Machida-shi, Tokyo, Japan. (Received June 10, 1974; )     

Demonstration of light-induced potential change in Chara cells lacking tonoplast

Chara cells without tonoplasts, prepared by replacing the cellsap with EGTA-containing media, showed essentially the samepattern of light-induced changes in membrane potential and membraneresistance as normal cells although the concentrations of ionsand ATP in the cytoplasm decreased considerably (1/3–1/10)after loss of the tonoplast. Removal of the tonoplast reducedthe rate of photosynthetic O₂ evolution to about 50% of thatof normal cells but did not affect the magnitude of light-inducedpotential change. Not a full but a certain level of electronflow seems necessary to activate the putative electrogenic H⁺-pump. ¹ Present address: Department of Botany, Faculty of Science,University of Tokyo, Japan. ² Present address: Niigata College of Pharmacy, Niigata 950-21,Japan. (Received September 4, 1978; )     

Lipid Biosynthesis in the Blue-Green Alga (Cyanobacterium), Anabaena variabilis III. UDPglucose:Diacylglycerol Glucosyltransferase Activity in vitro

The synthesis of glyceroglycolipids was studied in membraneand soluble fractions of Anabaena variabilis. The membrane fractionexhibited a high activity of UDPglucose: diacylglycerol glucosyltransferase,but practically no activity of UDPgalactose: diacylglycerolgalactosyltransferase. The glucosyltransferase activity wasmaximal at about pH 7.0 and dependent on Mg²⁺ The Michaelisconstant (K_m) for UDPglucose was 45?10^–6 M. The solublefraction catalyzed the incorporation of galactose from UDP galactoseinto digalactosyl diacylglycerol. These in vitro results werecompatible with the biosynthetic pathway of glyceroglycolipidsin this alga that we previously elucidated on the basis of tracerexperiments in vivo. ¹ Present address: Department of Biology, Faculty of Science,University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan. (Received June 1, 1982; Accepted July 1, 1982)     

The enzyme system for the entrance of 14CO2 in the dark CO2-fixation of brown algae

High activity of phosphoenolpyruvate (PEP)-carboxykinase, orADP: oxalacetate (OAA) carboxy-lyase activity (a kind of EC4. 1. 1. 32) was discovered in enzyme extracts or partiallypurified preparations obtained from the brown algae, Eiseniabicyclis, Dictyota dichotoma, Spatoglossum pacificum; and Hizikiafusiformis. Enzyme activities were determined by measuring theradioactivity incorporated in the products of dark ¹⁴CO₂-fixationand by spectrophotometric determinations. Except for the lowactivity of "malic enzyme" (EC 1. 1. 1.40), no activities ofother carboxylases, i.e. PEP-carboxylase, PEP-carboxytransphosphorylase,and pyruvate carboxylase could be detected in algal extractsprepared under various conditions. Malate dehydrogenase (EC1. 1. 1. 37), fumarase (EC 4. 2. 1. 2), and glutamic: oxalacetictransaminase (EC 2. 6. 1. 1) were also detected. The algal PEP-carboxykinase required ADP and Mn²⁺ for maximumactivity in the carboxylation reaction; and ATP and Mn²⁺, butnot GTP, for maximum activity in both the decarboxylation andOAA-¹⁴CO₂-exchange reactions. The optimum pH of purified PEP-carboxykinase was in the regionof 7.0 to 7.3 in both the carboxylation and decarboxylationreactions, and its Km values for HCO₃^–, PEP, and ADP were10 mM, 0.3 mM, and 0.07 mM, respectively, in the carboxylationreaction, and values for OAA and ATP were 0.05 mM and 0.4 mM,respectively, in the decarboxylation reaction. Furthermore,the decarboxylation reaction was markedly inhibited by 20 mMHCO₃^–. The physiological role of PEP-carboxykinase as the enzyme responsiblefor the entrance reaction of the dark CO₂-fixation is discussed. ¹ Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 236. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and Matsunaga Science Foundation (to T.Ikawa). ² Present address: Department of Antibiotics, the National Instituteof Health, Shinagawa, Tokyo, Japan. (Received February 22, 1972; )     

Comparison of carbon dioxide fixation and the fine structure in various assimilatory tissues of Amaranthus retroflexus L

The pattern for primary products of CO₂-fixation and the chloroplaststructure of Amaranthus retrqflexus L., a species which incorporatescarbon dioxide into C₄ dicarboxylic acids as the primary productof photosynthesis, were compared in various chlorophyll containingtissues,i.e., foliage leaves, stems, cotyledons and pale-greencallus induced from stem pith. Despite some morphological differencesin these assimilatory tissues, malate and aspartate were identifiedas the major compounds labelled during a 10 sec fixation of¹⁴CO₂ in all tissues. Whereas, aspartate was the major componentin C₄-dicarboxylic acids formed in foliage leaves, malate predominatedas the primary product in stems, cotyledons and the pale-greencallus. The percentage of ¹⁴C-radioactivity incorporated intoPGA and sugar-P esters increased and ¹⁴C-sucrose was detectedin the prolonged fixation of ¹⁴CO₂ in the light, not only infoliage leaves, but also in stems and cotyledons. ¹ This work was supported by a Grant for Scientific ResearchNo. 58813, from the Ministry of Education, Japan. ² Present address: Institute of Applied Microbiology, Universityof Tokyo, Tokyo, Japan. ³ Present address: Department of Biochemistry, University ofGeorgia, Athens 30601. Georgia, U. S. A. (Received July 10, 1971; )     

Effect of Cytoplasmic Ca2+ on the Membrane Potential and Membrane Resistance of Chara Plasmalemma

Effects of cytoplasmic Ca²⁺ on the electrical properties ofthe plasma membrane were investigated in tonoplast-free cellsof Chara australis that had been internally perfused with media,containing either 1 mM ATP to fuel the electrogenic pump orhexokinase and glucose to deplete the ATP and stop the pump. In the presence of ATP, cytoplasmic Ca²⁺ up to 2.5?10^–5M did not affect the membrane potential (about -190 mV), butmembrane resistance decreased uniformly with increasing [Ca²⁺]_i.In the absence of ATP, the membrane potential, which was onlyabout -110 mV, was depolarized further by raising [Ca²⁺]_i from1.4?10^–6 to 2.5?10^–5 M. Membrane resistance, whichwas nearly the twofold that of ATP-provided cells, decreasedmarkedly with an increase in [Ca²⁺]_i from zero to 1.38?10^–6M, but showed no change for further increases. Internodal cellsof Nitellopsis obtusa were more sensitive to intracellular Ca²⁺with respect to membrane potential than were those of Charaaustralis, reconfirming the results obtained by Mimura and Tazawa(1983). The effect of cytoplasmic Ca²⁺ on the ATP-dependent H⁺ effluxwas measured. No marked difference in H⁺ effluxes was detectedbetween zero and 2.5?10^–5 M [Ca²⁺]_i; but, at 10^–4M the ATP-dependent H⁺ efflux was almost zero. Ca²⁺ efflux experimentswere done to investigate dependencies on [Ca²⁺]_i and [ATP]_i.The efflux was about 1 pmol cm^–2 s^–1 at all [Ca²⁺]_iconcentrations tested (1.38?10^–6, 2.5?10^–5, 10^–4M).This value is much higher than the influx reported by Hayamaet al. (1979), and this efflux was independent of [ATP]_i. Thepossibility of a Ca²⁺-extruding pump is discussed. ¹ Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, 5300 Bonn, F.R.G. (Received September 22, 1984; Accepted February 19, 1985)     

Metabolism of [14C]GA20 in a Cell-Free System from Developing Seeds of Phaseolus vulgaris L.

The metabolism of [¹⁴C]GA₂₀ during seed maturation of Phaseolusvulgaris was studied using cell-free systems from embryos rangingin age from 10 DAF (day after flowering) to 24 DAF. Enzyme preparationsfrom very immature seeds actively converted GA₂₀ to GA¹, GA₅and GA₆. The ratio of incubation products suggested the biosyntheticpathway of GA₂₀—GA₅—GA₆. Fluctuation in the levelsof endogenous C₁₉-GAs, namely GA₁, GA₄, GA₅, GA₆, GA₈, GA₉ andGA₂₀ was analyzed by GC-SIM using internal standards to compareenzyme activity with the levels of endogenous GAs. AlthoughGA₁, GA₄ and GA₆ showed maximum levels on 20 DAF, enzyme activitydecreased during seed maturation and showed weak activity on20 DAF. ¹Graduate student of the University of Tokyo, Department ofAgricultural Chemistry, Bunkyo-ku, Tokyo 113, Japan. ³Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., Takarazuka, Hyogo655, Japan. (Received December 17, 1987; Accepted March 30, 1988)     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues1: XVII. THE EFFECT OF IODOACETATE ON THE CO2 OUTPUT, PATHWAYS OF GLUCOSE RESPIRATION AND CONTENTS OF PHOSPHATE ESTERS IN STRAWBERRY LEAVES

When specifically labelled glucose was fed to strawberry leaves,the C₆/C₁, quotient (rate of release of ¹⁴CO₂ from glucose-6-¹⁴C/rateof release of ¹⁴CO₂ from glucose-1¹⁴C ranged from 0.27 to 0.35in leaves in water and from 0.46 to 0.96 in leaves fed withiodoacetate. These quotients indicate that both the glycolyticand the pentose phosphate pathways participate in the respirationof strawberry leaves, with a greater contribution from the formerin the iodoacetate increased CO₂ output. Concurrently with the increase of CO² output in iodoacetate,the contents of glucose-6-phosphate (G6P), fructose-6 (F6P)and fructose-1,6-diphosphate (FDP) increased greatly; therewas a smaller increase of phosphoenol-pyruvate (PEP). The increasein the CO₂ output in iodoacetate may be explained solely onthe basis that the increases of G6P and FDP accelerate the ratesrespectively of the pentose phosphate pathway and of glycolysisand traffic into the tricarboxylic acid cycle. The increasein content of G6P and FDP is attributed to an increase in theaccessibility of enzymes and substrates caused by iodoacetate.Alternatively the increased CO₂ output in iodoacetate may bepartly due to uncoupling of oxidative phosphorylation.     

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; )     

Some further studies on metabolism of acetate-l-14C in potassium deficient rice leaves

Acetate-1-¹⁴C was fed to excised leaves of normal and potassiumdeficient rice plants. The rate of respiratory evolution of¹⁴CO₂ was increased by a potassium deficiency. Malonate, glyoxylateor malate supplied enhanced the metabolism of acetate-l-¹⁴C.These results suggest an accelerated turn of the TCA cycle inpotassium deficient leaves. Malate synthetase activity was notrecognized in either normal or deficient leaves. However, condensingenzyme activity was higher in deficient leaves than in normalones. An addition of DNP to the leaves increased ¹⁴CO₂ productionfrom acetate-l-¹⁴C though its effect was smaller in deficientleaves than it was in normal ones. This result may suggest anincrease in the turnover rate of ATP or loose coupling of electrontransfer with oxidative phosphorylation in deficient leaves.Chromatographic separation of cold acidsoluble nucleotides hasshown that the ATP level was lowered by a potassium deficiency,though the ADP level was not affected. ¹Present address: Sericultural Experiment Station, Suginami-Ku,Tokyo     

Energy conversion and changes in physical parameters in chloroplasts and subchloroplast particles II. Energy conversion in chloroplasts and different types of subchloroplast particles

The light-induced absorbance change at 515 nm, light-inducedhydrogen ion uptake and ATP formation were compared in chloroplastsand different types of sonicated subchloroplast particles. Noparallel relationship among the activities for ATP formation,hydrogen ion uptake and the 515-nm change was observed in differenttypes of preparations. NH₄Cl inhibited ATP formation in chloroplastsbut had little effect on subchloroplast particles. In contrast,the light-induced hydrogen ion uptake was inhibited by NH₄Clin a similar manner. Tetraphenylboron (TPB), at 1 µM, inhibited ATP formationby about 30% in both chloroplasts and subchloroplast particles.In the presence of TPB, ATP formation in chloroplasts was stronglyinhibited by NHC₄Cl, but in subchloroplast particles the additionalinhibitory effect of NH₄Cl was small. A synergistic inhibitionof photophosphorylation by valinomycin plus NH₄Cl was much clearer.Although acceleration of the recovery of the 515-nm change byNH₄Cl or valinomycin was moderate, the 515-nm change virtuallydisappeared when NH₄Cl and valinomycin were added simultaneously. Although the membrane potential has a major role as the principaldriving force for ATP formation in subchloroplast particles,the simultaneous abolishment of the pH gradient and membranepotential may be required to uncouple ATP formation. ¹Present address: Fukuoka Women's University, Kasumigaoka, Fukuoka813, Japan. ²Present address: Ryukyu University, Naha, Okinawa 903, Japan. (Received February 5, 1974; )     

Glycine-serine transformation in the photosynthetic bacterium Chromatium vinosum

The metabolic transformation of glycine into serine in the photosyntheticbacterium Chromatium vinosum was accompanied by the evolutionof CO₂ due to decarboxylation of glycine. Isonicotinylhydrazideinhibited both ¹⁴CO₂ evolution and the formation of ¹⁴C-serinefrom ¹⁴C-glycine. The results indicate that a glycine-serinetransformation reaction takes place which is analogous to thatoccurring in green leaf tissues. Glycine may be metabolisedthrough serine by this reaction. The light stimulation of ¹⁴CO₂evolution and ¹⁴C-serine formation from 14C-glycine by the Chromatiumcells are judged to be results of the light-induced enhancementof ¹⁴C-glycine uptake by the bacterial cells. ¹This is paper 53 in the series "Structure and Function of ChloroplastProteins" and paper 7 of the series "Biosynthetic Mechanismof Glycolate in Chromatium". Paper 6 of the latter series isRef. 3 by Asami and Akazawa (1978). ²This study was aided by research grants from the Ministry ofEducation, Science and Culture of Japan and the Nissan ScienceFoundation (Tokyo). ³Postdoctoral Fellow (1980) of the Japan Society for the Promotionof Science. (Received May 20, 1980; )