Control of misses in oxygen evolution by the oxido-reduction state of plastoquinone in Dunaliella tertiolecta

The way misses happen in oxygen evolution is subject to debate (Govindjee et al. 1985). We recently observed a linear lowering of the miss probability with the flash number (Meunier and Popovic 1989). Therefore, we investigated in Dunaliella tertiolecta the link between the average miss probability and the redox state of plastoquinone after n flashes. The effect of flashes was to oxidize the plastoquinone pool; we found that the oxidation of plastoquinone highly correlated (linear regression: R ²=0.996) with the lowering of the miss probability. The flash frequency was found to affect both the miss probability and the redox state of plastoquinone. When pre-flashes were given using a high flash frequency (10 Hz), the plastoquinone pool was oxidized and misses were low; however, if long dark intervals between flashes were used, the oxidizing effect of flashes was lost and the misses were high. We could not explain our results by assuming equal misses over all S-states; but unequal misses, caused by deactivations, were coherent with our results. We deduced that chlororespiration was responsible for the reduction of plastoquinone in the dark interval between flashes. We compared oxygen evolution with and without benzoquinone, using a low flash frequency (0.5 Hz) for maximum misses. Benzoquinone lowered the misses from 34% to 3%, and raised the amplitude of oxygen evolution by more than a factor of two (2). From this we deduced that the charge carrier C postulated to explain misses (Lavorel and Maison-Peteri 1983) did not account for more than 3% of miss probability in Dunaliella tertiolecta. These results indicate that the misses in oxygen evolution are controlled by the redox state of plastoquinone, through deactivations.     

Sugar nucleotides dissipate ATP-generated transmembrane pH gradient in Golgi vesicles from suspension-cell protoplasts ofChenopodium rubrum L.

A microsomal vesicle fraction (GV) markedly enriched by the Golgi marker enzyme latent inosine diphosphatase (IDPase) has been isolated from photoautotrophic suspension-cell protoplasts ofChenopodium rubrum L. Addition of ATP creates a substantial pH gradient across the GV membrane as measured by accumulation of acridine orange. The GV showed a density of 1.14 g·cm^-3 by equilibrium density centrifugation on sucrose gradients. Coincidence of acridine-orange accumulation and IDPase activity was confirmed on Percoll gradients. Formation of the pH gradient half-saturates at 0.3 mM MgATP, peaks at pH 7, and is competitively inhibited by ADP (k _i0.1 mM), but not by P_i; it is hardly inhibited by orthovanadate, quickly dissipated by monensink ₂=18 nM), nigericin (k _1/2=25 nM), and sluggishly by N-ethylmaleimide (k _1/235 M). Inhibition by KNO₃ (k _1/26.7 mM) is incomplete (60%). Uridine 5-diphosphate (UDP)-glucose, UDP-galactose, but not UDP-mannose and the pertinent sugars, dissipate the ATP-generated pH gradient (k _1/210–20 mM UDP-glucose; optimum pH at 7.8). This UDP-glucose activity is accompanied by release of P_i, but not of glucose or sucrose. UDP-glucoseinduced P_i release from the GV saturates (k _1/2=1 mM UDP-glucose; optimum pH at 7) and is completely inhibited by the anion-channel blocker 4,4-diisothiocyano-2,2-stilbene disulfonic acid (DIDS;k _1/2=140 M). The GV incorporates UDP-[U-¹⁴C]glucose into an acid-labile, alkaline-stable macromolecular compound; this process is like-wise inhibited by DIDS. We propose a model including, inter alia, a UDP-glucose/uridine-5-monophosphate translocator and a phosphate-permeable anion channel to operate in Golgi vesicles ofChenopodium rubrum.Abbreviations AO acridine orange - DIDS 4,4-diisothiocyano-2,2-stilbene disulfonic acid - FCCP carbonyl cyanidep-trifluoromethyoxyphenyl hydrazone - GV Golgi-vesicle-enriched microsomal fraction - IDPase mosine diphosphatase     

Studies on the deconvolution of flash-induced absorption changes into the difference spectra of individual redox steps within the water-oxidizing enzyme system

The possibility to determine the difference spectra _i+1j of each univalent redox step S_iS_i+1(i=0,...3) of the water-oxidizing enzyme system was analyzed by theoretical calculations and by measurements of 320 nm absorption changes induced by a train of saturating laser flashes (FWHM:7 ns) in PS II membrane fragments. It was found: a) Lipophilic quinones complicate the experimental determination of optical changes due the S_i-state transitions because they lead to an additional binary oscillation probably caused by a reductant-induced oxidation of the Fe²⁺ at the PS II acceptor side. b) In principle, a proper separation can be achieved at sufficiently high K₃[Fe(CN)₆] concentrations. c) An unequivocal deconvolution into the difference spectra _i+1j of flash train-induced optical changes which are exclusively due to S_i-state transitions is impossible unless the Kok parameters , and [S_i]₀ can be determined by an independent method.Measurements of the oxygen yield induced by a flash train reveals, that in thylakoids and PS II membrane fragments S_i is the stable state of dark adapted samples even at alkaline pH (up to pH=9). However, in PS II membrane fragments at pH>7.7 the misses probability markedly increases, in contrast to the properties of intact thylakoids. Based on these data the possibility is discussed that an equilibrium exists of two types of S₂-states with different properties.Abbreviations DCIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - Q_A.Q_B primary and secondary plastoquinone of PS II - Ph-p-BQ phenyl-p-benzoquinone - PS II photosystem II - S₁ redox state of the catalytic site of water oxidation - Z redox component connecting P680 with the catalytic site of water oxidation Presented at the Japan/US Binational Seminar on Solar Energy Conversion: Photochemical Reaction Centers and Oxygen Evolving Complexes of Plant Photosynthesis, Okazaki, Japan, March 17–21, 1987.     

Polynucleotides and Their Components in the Processes of Aromatic Nucleophilic Substitution: II.1 Nucleophilic Modification of 3′,5′-Bis-O- (α,β,α′,β′-tetrafluoropyrid-γ-yl)thymidine

The interaction of 3,5-bis-O-(,,,-tetrafluoropyrid--yl)thymidine with various nucleophilic reagents was studied to evaluate the possibility of molecular design of new types of nucleic acid analogues using S _NAr reactions. The reactions with morpholine and sodium azide led to the introduction of one and two nucleophilic residues into each of the polyfluorinated pyridine rings. The nucleophilic polycondensation with bifunctional reagents ethylenediamine and hexamethylenediamine depended on the nature of nucleophile and reaction conditions and resulted in the formation of supramolecules containing about five or more than 20 pyrimidine bases.     

Variability in the 11S globulin fraction of seed storage proteins ofHelianthus (Asteraceae)

The seed storage globulins from sixHelianthus and four hybrids were studied using mono and bidimensional gel SDS electrophoresis (+ 2 mercaptoethanol). The polypeptide composition of each subunit was determined. Different pairs are specifically expressed according to the species studied. Three typical patterns were discriminated. All the studied species exhibit five subunits: two of them are expressed in all the species (₁₁ and ₂₂). The subunit corresponding to the ₁₁ pair is present inH. petiolaris and in the three populations ofH. annuus studied. The _2b2 pair is common toH. annuus andH. argophyllus. H. petiolaris presents two specific _2a2 and ₄₄ pairs andH. annuus a specific ₃₃ pair. InH. argophyllus _{11 33} or ₄₄ are never observed but are replaced by ₁₃ and ₃₁ pairs. Some globulins, poorly represented, are of forms but present chains of higher molecular weights (in the range 54–56 kDa). Expressing variations in the banding patterns between these species by the use of a similarity index reveals complete identity between the three populations ofH. annuus. Identity between the twoH. petiolaris studied is also observed.H. annuus andH. argophyllus appear to be closer to each other thanH. petiolaris concerning the seed storage globulins.     

Somaclonal variant UC-T3: the expression of Fusarium wilt resistance in progeny arrays of celery,Apium graveolens L.

Summary First generation (S₁) progeny, second generation (S₂) progeny, and backcross (BC) progeny of a celery (Apium graveolens L. var. dulce) somaclonal variant, UC-T3, were evaluated for resistance to the fungus Fusarium oxysporum f. sp. apii, race 2 (FOA₂). Chisquare analysis of S₁ progeny showed that the expression of resistance did not fit a single-locus model. S₂ progeny means were similar among families, except in a heavily infested field. The lowest ranking S₂ family in both the lightly infested and heavily infested fields was significantly more resistant to FOA₂ than individuals of the susceptible progenitor line Tall-Utah 527OR; therefore; it was concluded that the trait was heritable. The phenotypic distribution of the backcross progeny was broad, suggesting that the new resistance was conferred by at least two genes whose expression was dominant to susceptibility. The mean scores for disease resistance of the progeny of crosses between UC-T3 and the moderately resistant line, Tall-Utah 527OHK, generally equaled the resistance found among the progeny of the most resistant parent.     

A quantitative method for separating reaction components of CMP-sialic acid: Lactosylceramide sialyltransferase using Sep Pak C18 cartridges

A rapid procedure is described for the separation of CMP-sialic acid:lactosylceramide sialyltransferase reaction components using Sep Pak C₁₈ cartridges. The quantitative separation of the more polar nucleotide sugar, CMP-sialic acid, and its free acid from the less polar G_M3-ganglioside is simple and rapid relative to previously described methods. Recovery of G_M3 is optimized by the addition of phosphatidylcholine to the reaction mixture prior to the chromatographic step. Using rat liver Golgi membranes as a source of CMP-sialic acid: lactosylceramide sialyltransferase activity (G_M3 synthase; ST-1), the transfer of [¹⁴C] sialic acid from CMP-[¹⁴C] sialic acid to lactosylceramide can be quantified by this assay. The procedure is reliable and may be applicable to the isolation of ganglioside products in otherin vitro glycosyltransferase assays.Abbreviations G_M3 G_M3-ganglioside - II³NeuAc-LacCer NeuAc2-3Gal1-4Glc1-1Cer - G_D1a G_D1a-ganglioside, IV³NeuAc, II³NeuAc-GgOse₄Cer, NeuAc2-3Gal1-3GalNac1-4(NeuAc2-3)Gal1-4Glc1-1Cer - G_D3 G_D3-ganglioside, II³(NeuAc)₂LacCer, NeuAc2-8NeuAc2-3Gal1-4Glc1-1Cer - GgOse₄Cer asialo-G_M1 Gal1-3GalNAc1-4Gal1-4Glc1-1Cer - FucG_MI fucosyl-G_MI-ganglioside, Fuc1-2Gal1-3GalNAc1-4Gal1-4 Glc1-1Cer - ST-1 G_M3 synthase, CMP-sialic acid:lactosylceramide sialyltransferase - LacCer lactosylceramide, Gal1-4Glc1-1Cer - CMP-NeuAc cytidine 5-monophospho-N-acetylneuraminic acid - PC phosphatidylcholine - PMSF phenylmethylsulfonyl fluoride     

Inheritance and linkage relationships of glutamate oxaloacetate transaminase isoenzymes in apple

Summary Four zones of enzymatic activity for glutamate oxaloacetate transaminase (GOT) were found in apple tissue. A dimeric gene, GOT-1, determining the fastest migrating zone, was identified. Six alleles were found, including a near null allelle which produced detectable heterodimeric bands but not homodimeric bands. A marked deficit or absence of certain geno-types in all backcrosses and in some crosses between unrelated varieties was attributed to the close linkage (r=0.02±0.005) of GOT-1 with the incompatibility S locus. GOT-1 was also closely linked with the isocitrate dehydrogenase locus IDH-1 (0.03±0.01). Proposed incompatibility genotypes for four cultivars, and the linked GOT-1 alleles are Cox: S ₁ b/S ₂ d, Idared: S ₃ a/S ₄ c, Fiesta: S ₃ a/S ₂ d and Kent: S ₃ a/S ₁ b.The results reported in this paper are part of a PhD Thesis by the first author     

Increased erythritol production in Torula sp. by Mn2+and Cu2+

The production of erythritol and the erythritol yield from glucose by Torula sp. were improved, in increasing order, by supplementing with 10 mg MnSO₄4H₂O l^–1, 2 mg CuSO₄5H₂O l^–1, and both 10 mg MnSO₄4H₂O l^–1 and 2 mg CuSO₄5H₂O l^–1. Mn²⁺ decreased the intracellular concentration of erythritol, whereas Cu²⁺ increased the activity of erythrose reductase in cells. These results suggest that Mn²⁺ altered the permeability of cells, whereas Cu²⁺ increased the activity of erythrose reductase in cells.     

New Triterpene Glycosides from an Ulosa sp. Sponge

New triterpene glycosides, ulososides C, (20S,22S,23R,24S)-3,22,23-trihydroxy-3-O-(-D-glucopyranosyl)-32-nor-24-methyllanost-8(9)-ene-30-oic acid, D, (20S,22S,23R,24S)-3,22,23-trihydroxy-3-O-(-D-N-acetylglucosaminopyranosyl)-32-nor-24-methyllanost-8(9)-ene-30-oic acid, and E, (20S,22S,23R,24S)-3,22,23-trihydroxy-3-O-(-D-glucuronopyranosyl-(1 2)--D-arabinopyranosyl-32-nor-24-methyllanost-8(9)-ene-30-oic acid, were isolated from an Ulosa sp. sponge. Their structures were determined by spectral methods and chemical transformations. Specific features of their structures are discussed.     

The use of the isoenzymic marker gene Got-1 in the recognition of incompatibility S alleles in apple

The S incompatibility system of apple was confirmed through the application of the gene Got-1 for glutamate oxaloacetate transaminase as a marker for the S locus. The 11S alleles proposed by Kobel et al. (1939) were confirmed through anomalous segregations for Got-1 observed in 14 semi-compatible crosses and regular segregations observed in 2 fully compatible crosses. The S allele genotypes of Idared (S ₃ S ₇), Cox (S ₅ S ₉) and Fiesta (S ₃ S ₅) were determined and found to fall within the original series. By associating parental incompatibility genotypes with the segregation of Got-1 alleles, we were able to deduce the coupling of S and Got-1 alleles in 9 varieties.     

Binary oscillations in the Kok model of oxygen evolution in oxygenic photosynthesis

The flash-induced kinetics of various characteristics of Photosystem II (PS II) in the thylakoids of oxygenic plants are modulated by a period of two, due to the function of a two-electron gate in the electron acceptor side, and by a period of four, due to the changes in the state of the oxygen-evolving complex. In the absence of inhibitors of PS II, the assignment of measured signal to the oxygen-evolving complex or to quinone acceptor side has frequently been done on the basis of the periodicity of its flash-induced oscillations, i.e. four or two. However, in some circumstances, the period four oscillatory processes of the donor side of PS II can generate period two oscillations. It is shown here that in the Kok model of oxygen evolution (equal misses and equal double hits), the sum of the concentrations of the S ₀ and S ₂ states (as well as the sum of concentrations of S ₁ and S ₃ states) oscillates with period of two: S ₀+S ₂S ₁+S ₃S ₀+S ₂S ₁+S ₃. Moreover, in the generalized Kok model (with specific miss factors and double hits for each S-state) there always exist such ₀, ₁, ₂, ₃ that the sum ₀[S₀] + ₁[S₁] + ₂[S₂] + ₃[S₃] oscillates with period of two as a function of flash number. Any other coefficients which are linearly connected with these coefficients, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbew7aLzaaja% aaaa!3917!\[\hat \varepsilon \]_i = c_1i + c₂, also generate binary oscillations of this sum. Therefore, the decomposition of the flash-induced oscillations of some measured parameters into binary oscillations, depending only on the acceptor side of PS II, and quaternary oscillations, depending only on the donor side of PS II, becomes practically impossible when measured with techniques (such as fluorescence of chlorophyll a, delayed fluorescence, electrochromic shift, transmembrane electrical potential, changes of pH and others) that could not spectrally distinguish the donor and acceptor sides. This property of the Kok cycle puts limits on the simultaneous analysis of the donor and acceptor sides of the RC of PS II in vivo and suggests that binary oscillations are no longer a certain indicator of the origin of a signal in the acceptor side of PS II.Abbreviations PS II Photosystem II - P680 primary electron donor of reaction center of PS II - Q_A one electron acceptor plastoquinone - Q_B two electron acceptor plastoquinone - S _n redox state of the oxygen evolving complex, where n=0,1,2,3 and 4 - Chl a chlorophyll a This paper is dedicated to the memory of Alexander Kononenko.     

Absorbance difference spectra of the S-state transitions in Photosystem II core particles

Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S₀ S₁ S₂ S₃ S₀, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S₃ state with an inactive state, perhaps related to Ca²⁺-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S₁ S₂ transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S₂ S₃ transition was similar to that reported by Lavergne 1991 for PS II membranes. The S₀ S₁ transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.Abbreviations Bis-Tris (bis[2-hydroxyethyl]imino-tris[hydroxymethyl]methane) - DCBQ 2,5-dichloro-p-benzoquinone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PS II Photosystem II - Q_A secondary electron acceptor of PS II - S₀ to S₄ redox state of the oxygen evolving complex - Z secondary electron donor of PS II     

Somatic embryogenesis from leaf cultures of potato

An efficient procedure has been developed for inducing somatic embryogenesis from leaf cultures of potato cv. Jyothi. Leaf sections were initially cultured on 2,4-dichlorophenoxyacetic acid (2,4-D) + benzyladenine (BA) and -naphthaleneacetic acid (NAA) + BA supplemented Murashige and Skoog (MS) media. Nodular embryogenic callus developed from the cut ends of explants on media containing 2,4-D and BA, whereas compact callus developed on media containing NAA and BA. The explants with primary callus were subsequently moved onto MS media containing zeatin and/or gibberellic acid (GA₃) and BA. Treatment with zeatin (22.8 M) and BA (10.0 M) resulted in the induction of the highest number of somatic embryos directly from meristematic centres produced on the nodular tissue. Embryo induction and maturation took place on this medium. The cotyledonary stage embryos developed into complete plantlets on hormone-free MS medium. A distinct feature of this study is the induction of somatic embryogenesis in leaf cultures of potato which has not been reported previously.     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Interaction of cytochrome c L with methanol dehydrogenase from Methylophaga marina 42:

The reaction of methanol dehydrogenase with cytochrome c _L from Methylophaga marina and the reactions of the non-physiological substrates, Wurster's blue and ascorbic acid, with both proteins were studied as a function of temperature (4–32 °C), pressure (1–2000 bar) and ionic strength using the optical high pressure stopped-flow method. The thermodynamic parameters H, S and V were determined for all reactions where electron transfers are involved. These data allowed the determination of the Maxwell relationships which proved the internal thermodynamic consistency of the system under study. A conformational change on the cytochrome c _L level was deduced from both breaks in the Arrhenius plots and the variation of the V with temperature.Abbreviations MOPS 4-morpholinepropanesulfonic acid - CHES 2-(cyclohexylamino)ethanesulfonic acid - MDH methanol dehydrogenase - EDTA ethylenedinitrilotetraacetic acid disodium salt - BTB bromothymol blue (3,3-dibromothymolsulfoneph-thalein) - PQQ 2,7,9-tricarboxy-lH-pyrrolo-[2,3f]quinoline-4,5-dione - cytochrome c _HH mammalian horse heart cytochrome c     

Isolation and Properties of a New Kallikrein Inhibitor from Tityus serrulatus Venom

The kallikrein inhibitor-peptide content of Tityus serrulatus scorpion crude venom was purified by Sephadex G-50 and Sephadex G-25 fine gel filtration chromatographies, followed by two steps of reverse-phase column on HPLC. The isolated inhibitor peptide was homogeneous in its N-terminal and partial amino acid sequence, showing a molecular weight of 4.489 Da by mass spectrometry and amino acid analysis. The peptide was tested with rat plasma and urine kallikrein, which resulting in an inhibition with similar afinity to both enzymes, showing an IC₅₀ of 14.3 M after 13 and 8 min, respectively, using kininogen as substrate on the isolated guinea-pig ileum bioassay. The porcine pancreatic kallikrein showed after 10 min an IC₅₀ value of 12.6 M with H-D-Val-Leu-Arg-pNA HCl as substrate. In addition, the isolated peptide significantly inhibited porcine pancreatic kallikrein with values in the range of apparent or absolute calculated peptide K _i = 2.5 M. The inhibitor was heat resistant and stable at pH values less than 5.     

Photosynthetic formation of inorganic pyrophosphate in phototrophic bacteria

In this paper we report studies on photosynthetic formation of inorganic pyrophosphate (PP_i) in three phototrophic bacteria. Formation of PP_i was found in chromatophores from Rhodopseudomonas viridis but not in chromatophores from Rhodopseudomonas blastica and Rhodobacter capsulatus. The maximal rate of PP_i synthesis in Rps. viridis was 0.15 mol PP_i formed/(min*mol Bacteriochlorophyll) at 23°C. The synthesis of PP_i was inhibited by electron transport inhibitors, uncouplers and fluoride, but was insensitive to oligomycin and venturicidin. The steady state rate of PP_i synthesis under continuous illumination was about 15% of the steady-state rate of ATP synthesis. The synthesis of PP_i after short light flashes was also studied. The yield of PP_i after a single 1 ms flash was equivalent to approximately 1 mol PP_i/500 mol Bacteriochlorophyll. In Rps. viridis chromatophores, PP_i was also found to induce a membrane potential, which was sensitive to carbonyl cyanide p-trifluoromethoxyphenylhydrazone and NaF.Abbreviations BChl Bacteriochlorophyll - F₀F₁-ATPase Membrane bound proton translocating ATP synthase - FCCP Carbonyl cyanide p-trifluoromethoxyphenylhydrazone - H⁺-PPase Membrane bound proton translocating PP_i synthase - TPP⁺ Tetraphenyl phosphonium ion - TPB^- Tetraphenyl boron ion - Transmembrane electrical potential difference     

The photosynthetic F1-α3β3 and α1β1 catalytic core complexes

Minimal photosynthetic catalytic F₁() core complexes, containing equimolar ratios of the and subunits, were isolated from membrane-bound spinach chloroplast CF₁ and Rhodospirillum rubrum chromatophore RrF₁. A CF₁-₃₃ hexamer and RrF₁-₁₁ dimer, which were purified from the respective F₁() complexes, exhibit lower rates and different properties from their parent F₁-ATPases. Most interesting is their complete resistance to inhibition by the general F₁ inhibitor azide and the specific CF₁ inhibitor tentoxin. These inhibitors were earlier reported to inhibit multisite, but not unisite, catalysis in all sensitive F₁-ATPases and were therefore suggested to block catalytic site cooperativity. The absence of this typical property of all F₁-ATPases in the ₁₁ dimer is consistant with the view that the dimer contains only a single catalytic site. The ₃₃ hexamer contains however all F₁ catalytic sites. Therefore the observation that CF₁-₃₃ can bind tentoxin and is stimulated by it suggests that the F₁ subunit, which is required for obtaining inhibition by tentoxin as well as azide, plays an important role in the cooperative interactions between the F₁-catalytic sites.Abbreviations CF₀F₁ chloroplast F₀F₁ - CF₁ chloroplast F₁ - CF₁ chloroplast F₁ subunit - CF₁ chloroplast F₁ subunit - CF₁() a complex containing equal amounts of the CF₁ and subunits - MF₁ mitochondrial F₁ - RrF₀F₁ Rhodospirillum rubrum F₀F₁ - RrF₁ R. rubrum F₁ - RrF₁ R. rubrum F₁ subunit - RrF₁ R. rubrum F₁ subunit - RrF₁() a complex containing equal amounts of the RrF₁ and subunits - Rubisco Ribulose-1,5-bisphosphate carboxylase - TF₁ thermophilic bacterium PS3 F₁