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At least 19 recordsLinked to original sources
PubMed1975

Enzymes of glycollate formation and oxidation in two members of the rhodospirillacae (purple non-sulphur bacteria).

1. Phototrophic cultures of Rhodomicrobium vanielii do not excrete glycollate when gassed anaerobically with nitrogen plus carbon dioxide, although the addition of alpha-hydroxy-2-pyridine methanesulphonate (HPMS) results in the excretion of a trace amount of glycollate. The inclucion of low amounts of oxygen in this gas mixture results in marked glycollate excretion, higher rates occurring in the presence of HPMS. 2. Cell extracts of Rhodomicrobium vannielii, and also of Rhodospirillum rubrum, which excretes glycollate only under aerobic conditions in the light, catalyze the formation of glycollate from phosphoglycollate and also the oxidation of glycollate to glyoxylate.

2,6-Dichloroindophenol↗
PubMed1975

Water proton relaxation as a monitor of membrane-bound manganese in spinach chloroplasts.

First measurements of proton relaxation on chloroplast membranes are presented here. Experiments show that the water proton spin-lattice relaxation rate in chloroplast thylakoid membrane suspensions can be used to monitor membrane-bound manganese. The relaxation effect is reduced to 0.4 of its original value upon manganese extraction by washing with either alkaline Tris buffer or NH2OH/EDTA solution. Large increases in the proton relaxation rate are measured in the presence of reductants such as tetraphenylboron and NH2OH; oxidants such as potassium ferricyanide or 2,6-dichlorophenolindophenol lead to an decrease in this rate. These results suggest that manganese exists as a mixture of oxidation states in dark-adapted chloroplasts.

2,6-Dichloroindophenol↗
PubMed1976

Properties and function of clostridial membrane ATPase.

ATPase (ATP phosphohydrolase, EC 3.6.1.3) was detected in the membrane fraction of the strict anaerobic bacterium, Clostridium pasteurianum. About 70% of the total activity was found in the particulate fraction. The enzyme was Mg2+ dependent; Co2+ and Mn2+ but not Ca2+ could replace Mg2+ to some extent; the activation by Mg2+ was slightly antagonized by Ca2+. Even in the presence of Mg2+, Na+ or K+ had no stimulatory effect. The ATPase reaction was effectively inhibited by one of its products, ADP, and only slightly by the other product, inorganic phosphate. Of the nucleoside triphosphates tested ATP was hydrolyzed with highest affinity ([S]0.5 v = 1.3 mM) and maximal activity (120 U/g). The ATPase activity could be nearly completely solubilized by treatment of the membranes with 2 M LiCl in the absence of Mg2+. Solubilization, however, led to instability of the enzyme. The clostridial solubilized and membrane-bound ATPase showed different properties similar to the "allotopic" properties of mitochondrial and other bacterial ATPases. The membrane-bound ATPase in contrast to the soluble ATPase was sensitive to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). DCCD, at 10(-4) M, led to 80% inhibition of the membrane-bound enzyme; oligomycin ouabain, or NaN3 had no effect. The membrane-bound ATPase could not be stimulated by trypsin pretreatment. Since none of the mono- or divalent cations had any truly stimulatory effect, and since a pH gradient (interior alkaline), which was sensitive to the ATPase inhibitor DCCD, was maintained during growth of C. pasteurianum, it was concluded that the function of the clostridial ATPase was the same as that of the rather similar mitochondrial enzyme, namely H+ translocation. A H+-translocating, ATP-consuming ATPase appears to be intrinsic equipment of all prolaryotic cells and as such to be phylogenetically very old; in the course of evolution the enzyme might have been developed to a H+-(re)translocating, ATP-forming ATPase as probably realized in aerobic bacteria, mitochondria and chloroplasts.

2,6-Dichloroindophenol↗
PubMed1976

Multi-temperature effects on Hill reaction activity of barley chloroplasts.

1. The relationship between temperature and Hill reaction activity has been investigated in chloroplasts isolated from barley (Hordeum vulgare L. cv. Abyssinian). 2. An Arrhenius plot of the photoreduction of 2,6-dichlorophenolindophenol (DCIP) showed no change in slope over the temperature range 2--38degreesC. The apparent Arrhenius activation energy (Ea) for the reaction was 48.1 kJ/mol. 3. In the presence of an uncoupler of photophosphorylation, methylamine, the Ea for DCIP photoreduction went through a series of changes as the temperature was increased. Changes were found at 9, 20, 29 and 36degreesC. The Ea was highest below 9degreesC at 63.7 kJ/mol. Between 9 and 20degreesC the Ea decreased to 40.4 kJ/mol and again to 20.2 kJ/mol between 20 and 29degreesC. Between 29 and 36degreesC there was no further increase in activity with increasing temperature. The temperature-induced changes at 9, 20 and 29degreesC were reversible. At temperatures above 36degreesC (2 min) a thermal and largely irreversible inactivation of the Hill reaction occurred. 4. Temperature-induced changes in Ea were also found when ferricyanide was substituted for DCIP or gramicidin D for methylamine. The addition of an uncoupler of photophosphorylation was not required to demonstrate temperature-induced changes in DCIP photoreduction following the exposure of the chloroplasts to a low concentration of cations. 5. The photoreduction of the lipophilic acceptor, oxidized 2, 3, 5, 6-tetramethyl-p-phenylenediamine, also showed changes in Ea in the absence of an uncoupler. 6. The temperature-induced changes in Hill activity at 9 and 29degreesC coincided with temperature-induced changes in the fluidity of chloroplast thylakoid membranes as detected by measurements of electron spin resonance spectra. It is suggested that the temperature-induced changes in the properties and activity of chloroplast membranes are part of a control mechanism for regulation of chloroplast development and photosynthesis by temperature.

2,6-Dichloroindophenol↗
PubMed1976

Inhibitory effect of p-nitrothiophenol in the light on the photosystem II activity of spinach chloroplasts.

The treatment of spinach chloroplasts with p-nitrothiophenol in the light at acidic and neutral pH'S caused specific inhibition of the Photosystem II activity, whereas the same treatment in the dark did not affect the activity at all. The photosystem I activity was not inhibited by p-nitrothiophenol both in the light and in the dark. The inhibition was accompanied by changes of fluorescence from chloroplasts. As observed at room temperature, the 685-nm band was lowered by the p-nitrothiophenol treatment in the light and, at liquid nitrogen temperature, the relative height of the 695-nm band to the 685-nm band increased and the 695-nm band shifted to longer wavelengths. The action spectra for these effects of p-nitrothiophenol on the activity and fluorescence showed a peak at 670 nm with a red drop at longer wavelengths. It was concluded that the light absorbed by Photosystem II is responsible for the chemical modification of chloroplasts with p-nitrothiopehnol to causing the specific inhibition of Photosystem II.

2,6-Dichloroindophenol↗
PubMed1976

Separation of subchloroplast membrane particles by counter-current distribution.

Counter-current distribution in an aqueous Dextran-polyethylene glycol two-phase system has been used to fractionate membrane fragments obtained by press treatment of Class II chloroplasts. By the counter-current distribution technique membrane particles are separated according to their surface properties such as charge and hydrophobicity. The fractions obtained were analysed with respect to photochemical activities, chlorophyll and P-700 contents. The Photosystem II enrichment after counter-current distribution was better than that obtained by differential centrifugation of the disrupted chloroplasts. However, the best separation of Photosystem I and II enriched particles could be achieved if differential centrifugation was combined with the counter-current distribution technique. Each centrifugal fraction could be further separated into Photosystems I and II enriched fractions since the Photosystem II particles preferred the dextran-rich bottom phase while the Photosystem I particles preferred the polyethylene glycol-rich top phase. By this procedure it was possible, without the use of detergents, to obtain vesicles which were more enriched in Photosystem II as compared to intact grana stacks. The partition behaviour of undisrupted Class II chloroplasts and the Photosystem I centrifugal fraction was the same. This similarity indicated that the membrane which is exposed to the surrounding polymers by the Class II chloroplasts is the Photosystem I rich membrane of the stroma lamellae.

2,6-Dichloroindophenol↗
PubMed1977

Photooxidase system of Rhodospirillum rubrum. I. Photooxidations catalyzed by chromatophores isolated from a mutant deficient in photooxidase activity.

The aerobic photooxidations of reduced 2,6-dichlorophenolindophenol and of reaction-center bacteriochlorophyll (P-870) have been investigated in membrane vesicles (chromatophores) isolated from a non-phototrophic Rhodospirillum rubrum strain. In aerobic suspensions of wild-type chromatophores, continuous light elicits an increase of the levels of 2,6-dichlorophenolindophenol and of oxidized P-870, which reach steady-state values shortly after the onset of illumination. In contrast, light induces in mutant suspensions a transient increase of the levels of 2,6-dichlorophenol-indophenol and of oxidized P-870, which fall to low steady-state values within a few seconds. These observations suggest that the mutation has altered a redox constituent located on the low-potential side of the photochemical reaction center, between a pool of acceptors and oxygen. Since endogenous cyclic photophosphorylation is catalyzed by mutant chromatophores at normal rates, it appears that the constituent altered by the mutation does not belong to the cyclic electron-transfer chain responsible for photophosphorylation. However, the system which mediates the aerobic photooxidations and the cyclic system are not completely independent: endogenous photophosphorylation is inhibited by oxygen in wild-type chromatophores but not in mutant chromatophores; in addition, the inhibitor of cyclic electron flow, 2-heptyl-4-hydroxyquinoline-N-oxide, enhances the aerobic photooxidation of reduced 2,6-dichlorophenolindophenol by chromatophores from both strains. These results support a tentative branched model for light-driven electron transfer. In that model, the constituent altered in the mutant strain is located in a side electron-transfer chain which connects the cyclic acceptors to oxygen.

2,6-Dichloroindophenol↗
PubMed1977

Identification of S2 as the sensitive state to alkaline photoinactivation of photosystem II in chloroplasts.

1. Chloroplasts have been preilluminated by a sequence of n short saturating flashes immediately before alkalinization to pH 9.3, and brought back 2 min later to pH 7.8. The assay of Photosystem II activity through dichlorophenolindophenol photoreduction, oxygen evolution, fluorescence induction, shows that part of the centers is inactivated and that this part depends on the number of preilluminating flashes (maximum inhibition after one flash) in a way which suggests identification of state S2 as the target for alkaline inactivation. 2. As shown by Reimer and Trebst ((1975) Biochem. Physiol. Pflanz. 168, 225-232) the inactivation necessitates the presence of gramicidin, which shows that the sensitive site is on the internal side of the thylakoid membrane. 3. The electron flow through inactivated Photosystem II is restored by artificial donor addition (diphenylcarbazide or hydroxylamine); this suggests that the water-splitting enzyme itself is blocked. The inactivation is accompanied by a solubilization of bound Mn2+ and by the occurence of EPR Signal II "fast". 4. Glutaraldehyde fixation before the treatment does not prevent the inactivation which thus does not seem to involve a protein structural change.

2,6-Dichloroindophenol↗
PubMed1975

Studies of a halophilic NADH dehydrogenase. II. Kinetic properties of the enzyme in relation to salt activation.

1. An NADH dehydrogenase, obtained from an extremely halophilic bacterium, was activated by various salts when enzyme activity was measured as the observed velocity, whereas the maximum velocity was unaffected by either the salt concentration or the nature of the salt. 2. Two ion effects were observed; a quantitative cation effect, reflected in changes in the apparent Michaelis constant for 2,6-dichlorophenolindophenol, and a qualitative anion effect, reflected in the apparent Michaelis and dissociation constants for NADH. 3. The data suggest that cations act by neutralizing electrostatic charges surrounding the 2,6-dichlorophenolindophenol-binding site, whereas the anions affect the conformation of the enzyme by altering the accessibility of the NADH-binding site to the bulk solvent. 4. Thus, the apparent activation of this enzyme, obtained from an extremely halophilic bacterium, is a reflection of measuring enzyme activity at non-saturating substrate concentrations.

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