Genetic Analysis and Regulation of Bacteriochlorophyll Biosynthesis

Biel, A J

doi:10.1007/0-306-47954-0_52

Cited by 6 publications

(4 citation statements)

References 65 publications

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“…In wild-type cells of photosynthetic bacteria the synthesis of pigments and pigment-binding polypeptides is strictly corregulated on the transcriptional and posttranscriptional level (BIEL 1995, BAUER 1995, DREWS and GOLECKI 1995, KLUG 1995. Only small amounts of precursors of BChl were detectable in wild-type cells adapting to photosynthetic conditions (BECK and DREWS 1982).…”

Section: Discussionmentioning

confidence: 99%

“…Only small amounts of precursors of BChl were detectable in wild-type cells adapting to photosynthetic conditions (BECK and DREWS 1982). Mutants blocked at different steps of tetrapyrrol biosynthesis excrete precursors of BChl synthesis (LASCELLES 1966, DREWS 1974, BAUER et al 1993, BIEL 1995. Resonance Raman-, Fourier transform infrared studies and the crystal structures of pigment-proteins have shown that the BChl's interact with each other and with specific amino acids in the surrounding of the protein scaffold (LUTZ and MANTELE 1991, STURGIS and ROBERT 1996, FREER et al 1996.…”

Section: Discussionmentioning

confidence: 99%

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The role of pigments in the assembly of photosynthetic complexes in Rhodobacter capsulatus

Brand

Drews

1997

J. Basic Microbiol.

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Mutants of Rhodobacter cupsulatus, blocked at different steps of bacteriochlorophyll a (BChl) synthesis between protoporphyrin IX and 2-hydroxyethyl bacteriochlorophyllide a, were induced to synthesize the photosynthetic apparatus by lowering of oxygen tension in dark cultures. The cells were pulse-labeled with [''S]methionine and the radioactivity chased after dilution of PSI. The specific radioactivity in the pigment-binding proteins of light-harvesting and reaction center proteins of the wild-type strain was not lowered during the chase period of three hours but in the BChl-free mutants the label disappeared within five to thirty minutes. The polypeptides were inserted into the membrane but did not remain stably incorporated. In the mutant strain NK9 the synthesis of the carotenoid spheroidenonelspheroidene was inhibited by insertion of Tn5 in the CHI gene (phytoene desaturase), which blocked completely the formation of the light-harvesting (LH) complex I1 (B800-850) but not of the LHI (B870) complex. In this mutant the polypeptides of the LH complexes were synthesized in a lower amount than in the wild-type cells and were inserted into the membrane. The LHIIa polypeptide disappeared after 60 min of chase while the LHIIP was more stable. It was concluded that the pigments are not only necessary for absorption of photons and efficient transfer of excitation energy but have a structural role by stabilizing the oligomeric LH complexes. This is in accordance with the crystal structure data of LHII complexes.Photosynthetic organisms have two types of pigment-protein complexes, the lightharvesting (LH) or antenna complexes which absorb light quanta and funnel the resulting excited states to the photosynthetic reaction center (RC) where the primary donor is excited and a charge separation and a formation of an electrical potential across the membrane is initiated (DREWS 1992). In cells of Rhodobacter cupsulatus two types of LH complexes are present. LHI, which has the major absorption maximum at 870 nm, surrounds the RC in stoichiometric amounts and is the direct donor of excitation energy to the RC (core complex). LHII is the peripheral LH complex and has two major absorption bands at 800 and 850 nm (B800-850). The formation of the RC and LH complexes is induced by lowering of the oxygen partial pressure in the medium and is not light-dependent. But the light intensity determines the amount of pigment-proteins per cell and per membrane protein. Under high light intensity the synthesis of the LHII complex is particularly lowered and therefore the ratio of LHII/LHI-RC is variable (see review in DREWS and GOLECKI 1995). Bacteriochlorophyll a (BChl) and the carotenoids spheroidene/spheroidenone are bound non-covalently to the two pigment-binding polypeptide a and / 3 in LH complexes and to the subunits L and M in RC. Inhibition of BChl synthesis prevents the formation of the pigment-protein complexes (ISLUG et al. 1986). Crystal structures of LH and RC complexes have shown that the pigments interact with each other and ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The role of pigments in the assembly of photosynthetic complexes in Rhodobacter capsulatus

Brand

Drews

1997

J. Basic Microbiol.

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“…or aspects of regulation specific to multicellular organisms with complex developmental patterns were essentially omitted. A number of reviews reporting recent progress in various aspects of tetrapyrrole (Beale, 1993(Beale, , 1995Biel, 1995;von Wettstein et al, 1995;Fujita, 1996;Reinbothe and Reinbothe, 1996) and carotenoid (Bartley et al, 1994;Hirschberg and Chamovitz, 1994;Armstrong, 1995;Bartley and Scolnik, 1995;Armstrong and Hearst, 1996;Yamamoto and Bassi, 1996) formation in photosynthetic organisms have been published within the past few years. The reader is referred to these articles for additional information on aspects of the respective pathways not specifically addressed in this chapter.…”

Section: Introductionmentioning

confidence: 99%

Pigment Biosynthesis: Chlorophylls, Heme, and Carotenoids

Timko

Advances in Photosynthesis and Respiration

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“…It was demonstrated that light regulated the synthesis of Bchl: the Bchl levels were inversely proportional to light intensity in photosynthetically grown cultures (17). However, several pieces of evidence suggest that light intensity controls the rate of Bchl degradation rather than the rate of synthesis (18,19). The photodegradation of Bchl by oxygen and the protective role of carotenoid in this harmful process have been well documented (20–23), but much less effort has been devoted to studies of degradation in the absence of oxygen and carotenoids.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of Light‐induced and Thermal Degradation of Bacteriochlorins in Reaction Center Protein of Photosynthetic Bacteria

Tandori

Tokaji

Misurda

et al. 2005

Photochem & Photobiology

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The rate constants of thermal (irreversible) damage of bacteriochlorin pigments (bacteriochlorophyll monomer [B], bacteriochlorophyll dimer [P] and bacteriopheophytine [H]) in reaction center [RC] protein from the photosynthetic bacterium Rhodobacter sphaeroides were studied in the dark and during intense (400 mW x cm(-2)) laser light excitation (wavelengths 488 and 515 nm) under deoxygenated conditions. While the kinetics of degradation of P and B were monoexponential, the decay kinetics of H were overlapped by an initial lag phase at elevated (>40 degrees C) temperature. This is explained by removal of the central metal ion from the bacteriochlorophylls as part of their degradation processes. At all temperatures, the rates of damage were very similar for all bacteriochlorin pigments and were larger in the light than in the dark. The logarithm of the rate constant of pigment degradation and loss of photochemistry as a function of reciprocal (absolute) temperature (Arrhenius/Eyring plot) showed single phase in the light and double phases in the dark. Below 20 degrees C, the rate of pigment degradation in the RC decreased so dramatically in the dark that it became limited by the natural degradation process of bacteriochlorophyll measured in solution. The function of loss of photochemistry in the dark was also biphasic and had a break point at 40 degrees C. The damage in the dark required high enthalpy change (DeltaH(++) = 64 kcal/mol for P and DeltaH(++) = 60 kcal/mol for B) and entropy increase (T x DeltaS(++) = 38 kcal/mol for P and T x DeltaS(++) = 34 kcal/mol for B at T = 300 K), whereas significantly smaller enthalpy change (DeltaH(++) = 21 kcal/mol for P and B and DeltaH(++) = 13 kcal/mol for H) and practically no (T x DeltaS(++) = -1 kcal/mol for P and B at T = 300 K) or small (T x DeltaS(++) = -9 kcal/mol for H at T = 300 K) entropy change was needed in the light. The thermodynamic parameters of activation reveal major steps common in the degradation of all bacteriochlorin pigments: ring opening reactions at C5 or C20 meso-bridges (or both) and breaking/removal of the phytyl chain. Their contribution in the degradation is probably reflected in the observed enthalpy/entropy compensation at an almost constant (DeltaG(++) = 22-26 kcal/mol at T = 300 K) free energy change of activation.

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Genetic Analysis and Regulation of Bacteriochlorophyll Biosynthesis

Cited by 6 publications

References 65 publications

The role of pigments in the assembly of photosynthetic complexes in Rhodobacter capsulatus

The role of pigments in the assembly of photosynthetic complexes in Rhodobacter capsulatus

Pigment Biosynthesis: Chlorophylls, Heme, and Carotenoids

Thermodynamics of Light‐induced and Thermal Degradation of Bacteriochlorins in Reaction Center Protein of Photosynthetic Bacteria

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