Berger C. Mayne

Purification and initial characterization of phycobiliproteins from the endophytic cyanobacterium of Azolla

The endophytic cyanobacterium, Anabaena azollae, isolated from laboratory cultures of Azolla caroliniana Willd., contains three spectroscopically distinct biliproteins. About 70% of the biliprotein is c-phycocyanin (λmax 610 nm) and 13% is allophycocyanin (λmax 647 nm, shoulder 620 nm). A third pigment corresponds to phycoerythrocyanin (λmax 570 nm, shoulder 590 nm). In very dilute solutions of allophycocyanin, at constant pH and buffer strength, the 647 nm maximum disappears and a single λmax occurs at 615–620 nm. The 647 nm absorption maximum reappears upon concentrating the dilute solution. Very dilute solutions of phycoerythrocyanin exhibit a broad peak between 570 and 590 nm. Absorption spectra of c-phycocyanin are not significantly altered upon dilution. Fluorescence emission maxima of phycoerythrocyanin, c-phycocyanin, and allophycocyanin occur at 630 nm, 643 nm and 660 nm respectively, using 540 nm excitation. Two subunits, of molecular weight 16,500 (α) and 20,600 (β), are seen in c-phycocyanin upon dissociation with SDS. Dissociation of allophycocyanin and phycoerythrocyanin with SDS yields one sizeclass of subunits, with a molecular weight of about 17,500 for allophycocyanin and 18,000 for phycoerythrocyanin.

Chemically and Physically Induced Luminescence as a Probe of Photosynthetic Mechanisms

Publisher Summary This chapter discusses chemically and physically induced luminescence as a probe of photosynthetic mechanisms. From the moment of its discovery, it was hoped that delayed fluorescence would provide new insights into the mechanism of the early steps of quantum conversion by the photosynthetic apparatus. Luminscence studies have indeed furnished such information. But in addition, current studies indicate that delayed and induced fluorescence may provide sensitive probes of the storage of charge in photosystem II—the oxygen-evolving system of photosynthesis—and even of the state and structure of the photosynthetic membranes, and of the storage of the high energy intermediates that are used to drive photo-phosphorylation. The mechanisms of oxygen evolution and photo-phosphorylation have been among the more intractable and controversial problems in photosynthesis research. The fact that oxygen can cause bacteria to emit light suggested that luminescence might be evoked by other oxidants, such as ferricyanide; but reductants such as hydrosulfite could also be likely candidates

Further characterization of a photosystem ii particle isolated from spinach chloroplasts by triton treatment delayed light emission

Abstract Delayed light emission from the Triton-fractionated Photosystem II subchloroplast fragments (TSF-IIa) was measured between 0.5 and 10 ms after the termination of illumination. The delayed light emission was diminished by Photosystem II inhibitors, DCMU and o-phenanthroline, which act between the reduced primary acceptor and the plastoquinone pool. Secondary electron donors to Photosystem II, diphenylcarbazide, phenylenediamine, Mn2+, and ascorbate inhibited delayed light emission. Secondary electron acceptors such as ferricyanide, dichlorophenol indophenol, and dimethyl benzoquinone enhanced delayed light emission. The addition of secondary electron acceptors to TSF-IIa particles containing Mn2+ restored delayed light emission to almost the control level. The plastoquinone antagonist, 2,5-dibromo-3-methyl-6-isopropyl p-benzoquinone, increased delayed light emission at low concentrations but decreased it at higher concentrations. Silicomolybdate enhanced the delayed light emission of TSF-IIa particles markedly, and reversed the inhibition by DCMU. Silicomolybdate showed a similar stimulatory effect on the delayed-light intensity in broken spinach chloroplasts at shorter times after the termination of illumination. Carbonyl cyanide m-chloro (or p-trifluoromethoxy) phenylhydrazones inhibited the delayed light emission, but NH4Cl had no effect.

The subcellular localization of the pteridines in strain R-26 of Rhodopseudomonas spheroides☆

Pteridines were detected in strain R-26 of Rhodopseudomonas spheroides and the pteridine concentrations in subcellular fractions were measured by a sensitive fluorimetric method. The whole cell fraction contained nearly equal concentrations of pteridine and reaction center bacteriochlorophyll. The soluble subcellular fraction contained the majority of the pteridine and the photochemically active chromatophore preparations contained very little. No pteridine was detected in purified reaction center complex preparations. This subcellular localization of pteridines was not consistent with a pteridine functioning as the primary electron acceptor in this photosynthetic system.

Photosynthesis and the Biochemistry of Nitrogen Fixation

Nitrogen fixation is an energetically costly process. This is true whether we are referring to the production of ammonia by the Haber-Bosch process or by biological reactions.