Lettuce Chloroplasts Research Articles

Diaminodurene-induced plastocyanin dependent oxygen uptake and its relation to photophosphorylation in isolated lettuce chloroplasts. A comparison of the systems using either water or ascorbate as the electron donors.

1 Addition of diaminodurene induced in lettuce chloroplasts an oxygen uptake, which as a typical pseudocyclic electron transport was inhibited by 3-(3,4-dichlorophenol)-1,1-dimethylurea and stimulated by uncouplers. ATP formation was coupled to this electron transport from water through diaminodurene to oxygen, resulting in a P/2e value close to 1. 2 Diaminodurene induced also an oxygen uptake in the presence of dichlorophenol-dimethylurea and ascorbate, which was not affected by uncouplers. The rate of the oxygen uptake in this system changed as a function of diaminodurene concentration and was between 3 to 15 times faster than the oxygen uptake with water as the electron donor. The rate of ATP formation in this system was also dependent on the concentration of diaminodurene, but was much slower than the oxygen uptake, the resulting P/2e value being about 0.18. 3 Under argon a cyclic dichlorophenol-dimethylurea-resistant diaminodurene-dependent ATP formation was obtained. The rates of this cyclic phosphorylation were similar to those observed under air in the presence of ascorbate, although in the last case a ten-fold faster electron transport to oxygen accompanied the phosphorylation. 4 Sonication of the chloroplasts resulted in 85% inhibition of the diaminodurene-induced oxygen uptake when either water or ascorbate served as the electron donors. The inhibition was relieved by the addition of plastocyanin, which restored the original rates of oxygen uptake with both electron donors. 5 It is proposed that a free radical of diaminodurene, which is stabilized by interaction with a chloroplast component, possibly the ferredoxin reducing substance, is the compound acting as an autoxidizable electron acceptor upon addition of diaminodurene to lettuce chloroplasts.

The stimulation of post-illumination ATP synthesis by valinomycin

A high-energy state or intermediate (XE) is formed in illuminated chloroplasts which can drive ATP formation in a dark reaction [l] . Since the characteristics of X, and of the light-induced H+ uptake [2] are similar, it has been proposed that XE is a gradient in H+ activity across chloroplast membranes. This view is substantiated by the finding that ATP formation may be driven in total darkness by an artificiallyproduced H+ gradient [3]. Nelson et al. [4] reported that the treatment of lettuce chloroplasts with digitonin inhibited H+ uptake and post-illumination ATP synthesis more severely than photophosphorylation. In our previous studies on phosphorylation in subchloroplast particles [ 5,6] , we concluded that H+ uptake in these particles was electrogenic and, furthermore, that a membrane potential might play a role in photophosphorylation. To test this idea further, the effects of valinomycin and K+ on post-illumination ATP synthesis and H+ uptake in subchloroplast particles were tested. These reagents were found previously [7] to enhance H+ uptake in R.rubrum chromatophores. In this paper, we report that valinomycin in the presence of K+ stimulated H+ uptake as well as the formation of X, in subchloroplast particles.

Ferrochelatase of lettuce chloroplasts

Research Article| December 01 1968 Ferrochelatase of lettuce chloroplasts R F G J King; R F G J King 1Department of Biochemistry, University of Bath, and National Vegetable ResearchStation, Wellesbourne, Warwicks Search for other works by this author on: This Site PubMed Google Scholar E R Page E R Page 1Department of Biochemistry, University of Bath, and National Vegetable ResearchStation, Wellesbourne, Warwicks Search for other works by this author on: This Site PubMed Google Scholar Biochem J (1968) 110 (4): 45P. https://doi.org/10.1042/bj1100045Pa Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation R F G J King, E R Page; Ferrochelatase of lettuce chloroplasts. Biochem J 1 December 1968; 110 (4): 45P. doi: https://doi.org/10.1042/bj1100045Pa Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentAll JournalsBiochemical Journal Search Advanced Search This content is only available as a PDF. © 1968 The Biochemical Society1968 Article PDF first page preview Close Modal You do not currently have access to this content.

Stimulation of photoreactions of isolated chloroplasts by serum albumin.

Serum albumin was shown to stimulate markedly various photoreactions in isolated bean and lettuce chloroplasts. The maximal effect was obtained when this compound was present during the homogenization step and continuously in the chloroplast preparation. The "basal" electron transport was enhanced using various acceptors and stimulation was obtained also in the presence of uncouplers. The quantum requirement for ferricyanide reduction was appreciably reduced. Serum albumin increased the rate of cyclic phosphorylation and the ratio of P/e(2) in non-cyclic phosphorylation. The increase in phosphorylation is supposedly due to inhibition of the rate of decay of the high energy non-phosphorylated intermediate, X(E). It is postulated that serum albumin affects chloroplast photoreactions by binding endogenously released unsaturated fatty acids.

The catalysis by modified chloroplasts of the P i ↔ ATP, P i ↔ HOH and ATP ↔ HOH exchange reactions in the absence of light

P i ↔ HOH, ATP ↔ HOH and P i ↔ ATP exchanges, probably reflecting the phosphorylation and water formation reactions of photosynthetic phosphorylation are catalyzed in the dark by lettuce chloroplasts after exposure to light and dithiothreitol. A marked stimulation of the P i ↔ HOH exchange by ATP and of the ATP ↔ and of the ATP ↔ HOH exchange by P i, and a lack of ADP inhibition of the P i ↔ ATP and ATP ↔ HOH exchanges are consistent with all exchanges occurring by dynamic reversal of ATP cleavage at the catalytic site.

Fat metabolism in higher plants: XXXII. Control of plant acetyl-CoA carboxylase activity

Intact lettuce chloroplasts readily utilize acetate- 14C for incorporation into long chain fatty acids in the presence of HCO 3 − , ATP, Mg ++, and light. However, disrupted chloroplasts no longer utilize either acetate- 14C or acetyl-CoA- 14C as a substrate. Present investigations show an almost complete absence of acetyl-CoA carboxylase activity in preparations of disrupted chloroplasts. Attempts to stimulate this activity by employing the allosteric effectors of mammalian and yeast acetyl-CoA carboxylase gave negative results. Further study showed the presence of an inhibitor in preparations of disrupted chloroplasts which markedly depressed the activity of wheat germ acetyl-CoA carboxylase. Its general properties are described. In addition, wheat germ acetyl-CoA carboxylase, unlike its counterparts in other tissues, is not stimulated by phosphorylated sugars, dicarboxylic and tricarboxylic acids.

Fat metabolism in higher plants: XXXIX. Properties of a soluble fatty acid synthesizing system from lettuce chloroplasts

Fatty acid synthesis from malonyl-CoA was found to be greatly stimulated by the addition of acyl carrier protein (ACP), prepared from either lyophilized Escherichia coli cells or from avocado mesocarp. Likewise, heat-stable protein preparations from butter lettuce chloroplasts or butter lettuce leaves stimulate fatty acid synthesis. A heat-stable protein fraction termed lettuce ACP was prepared from butter lettuce leaves; it was active in the malonyl-CoA-CO 2 exchange reaction with E. coli enzymes and stimulated fatty acid synthesis with butter lettuce chloroplast-soluble enzymes. The ACP preparations from E. coli, butter lettuce, and avocado were all found to be similar in their activities in the CO 2 exchange reaction and in fatty acid synthesis. Preliminary evidence has been obtained which indicates that the fatty acid synthesizing system in butter head lettuce chloroplast-soluble enzymes preparation, as in E. coli extracts, can be resolved into a number of separate protein fractions which must be recombined for fatty acid synthesis.

A soluble fatty acid synthesizing system from lettuce chloroplasts

A soluble fatty acid synthesizing system from lettuce chloroplasts

Fat metabolism in higher plants XX. relation of fatty acid synthesis and photophosphorylation in lettuce chloroplasts

The incorporation of acetate into chloroplast lipids by illuminated chloroplasts in the presence of CoA, HCO 3-, Mg 2+, and Mn 2+, is stimulated by TPN when ADP and orthophosphate are present. p-Chlorophenyldimethylurea and NH 4+, inhibitors of photophosphorylation reactions, also decrease acetate incorporation. The system shows a requirement for orthophosphate. These results are interpreted to mean that acetate incorporation into fatty acids of chloroplasts depends on non-cyclic photophosphorylation which results in the formation of TPNH 2, ATP, and O 2. Cyclic photophosphorylation alone by which only ATP is photoproduced was not found to stimulate acetate incorporation. Acetate incorporation is increased when the reaction is carried out in air instead of nitrogen. The effect is more pronounced in the absence of TPN. These results are explained by the ability of oxygen to catalyze a non-cyclic photophosphorylation, and (or) by the role of oxygen as a cofactor in the synthesis of unsaturated fatty acids. Added TPNH 2, ATP and O 2 were not found to stimulate acetate incorporation in the dark.

Fat metabolism in higher plants XX. relation of fatty acid synthesis and photophosphorylation in lettuce chloroplasts

The incorporation of acetate into chloroplast lipids by illuminated chloroplasts in the presence of CoA, HCO 3-, Mg 2+, and Mn 2+, is stimulated by TPN when ADP and orthophosphate are present. p-Chlorophenyldimethylurea and NH 4+, inhibitors of photophosphorylation reactions, also decrease acetate incorporation. The system shows a requirement for orthophosphate. These results are interpreted to mean that acetate incorporation into fatty acids of chloroplasts depends on non-cyclic photophosphorylation which results in the formation of TPNH 2, ATP, and O 2. Cyclic photophosphorylation alone by which only ATP is photoproduced was not found to stimulate acetate incorporation. Acetate incorporation is increased when the reaction is carried out in air instead of nitrogen. The effect is more pronounced in the absence of TPN. These results are explained by the ability of oxygen to catalyze a non-cyclic photophosphorylation, and (or) by the role of oxygen as a cofactor in the synthesis of unsaturated fatty acids. Added TPNH 2, ATP and O 2 were not found to stimulate acetate incorporation in the dark.