ISSN:0021-2148    

DOI:10.1002/ijch.198100045

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractA brief review is given of the present knowledge of the mechanism by which higher plants and algae bring about the photooxidation of water. Emphasis is placed on the role of manganese in this process and a summary is given of recent efforts from several laboratories to isolate the “water‐splitting enzyme”. Experimental evidence is presented that, in contrast to earlier beliefs, the Mn not removed by washing chloroplast thylakoids with high concentrations of Tris (hydroxymethyl) amino methane could be involved in O2evolution. This manganese is equivalent to about 2 Mn per photosystem two reaction centre. Also presented are details of the isolation of a heme‐protein from spinach chloroplasts which may be intimately associated with the water splitting process. This protein has a native molecular weight of approximately 232 k Daltons and has characteristics similar to those of a catalase type enzyme. The possibility of involvement of peroxide formation during the water splitting process is di

ISSN:0021-2148    

DOI:10.1002/ijch.198100046

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractTwenty‐one quinone compounds have been tested for their ability to inhibit the primary photochemical events when added toR. rubrumchromatophores. This was determined by measuring their effect on the light‐induced absorbance change at 605 nm and their ability to quench the variable portion of fluorescence (Fv). Benzoquinone structures with one or more bromine or iodine substituents and a bulky group (isopropyl, t‐butyl, n‐hexyl) were particularly effective inhibitors. The most potent of these were 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone and 2,3‐diiodo‐5‐t‐butyl‐1,4‐benzoquinone which caused 50% inhibition at less than μM quantities (or about 5 to 10 fold above the phototrap concentrations). From control experiments with egg yolk phosphatidylcholine liposomes containing bacteriochlorophyll, it was shown that although the effective inhibitors also quenched fluorescence when added to this model system, quenching depended on the viscosity of the bilayer and was not very sensitive to structural parameters. In the in vivo system, phototrap activity was inhibited at 77 K to the same extent as room temperature, indicating diffusion was not important. In the control experiments with liposomes, the concentration for which 50% quenching was observed by 2,5‐dibromo‐3,6‐dimethyl‐1,4‐benzoquinone and 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone only differed by two fold whereas in the chromatophore system, the difference was over 1000 fold; no effect was seen in vivo by the former compound and the latter was the most effective. It is suggested that most of the instantaneous fluorescence (Fo) is from a bacteriochlorophyll component(s) which does not communicate with the reaction center and a higher concentration of added quinone is

ISSN:0021-2148    

DOI:10.1002/ijch.198100047

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractA number of amino acids and molecules of related functionality have been covalently connected to pyrochlorophyllidea(PChla) and bacteriopyrochlorophyllidea(BPChla) to determine their impact on the properties of the chromophore. PChlaand BPChlaesterified with side chains containing the thio‐ether functionality (methyl‐6‐hydroxyhexylsulfide, a Met analogue) were studied in detail by NMR. Intramolecular coordination at the central metal is observed for the Zn‐PChlaand Zn‐BPChlathio‐ether derivatives, but not for the Mg‐PChladerivative. The NMR data for the Zn‐PChladerivative is interpreted as providing evidence for two, distinguishable five‐coordinate complexes, with the ligand on either side of the macrocycle. In contrast, the Zn‐BPChladerivative appears to be coordinated exclusively on one side. It is proposed that stereoselective coordination may provide a simple mechanism for altering the spectroscopic properties of BChlawhen it binds to a protein. PChlawas covalently attached to the methyl esters of L‐Trp, L‐Tyr, L‐Phe and L‐Val. Very large, similar chemical shift changes in the NMR spectra in the absence of a coordinating ligand indicate that all of these compounds form a novel dimer, in which the carbonyl group of the carbomethoxy group on the amino acid coordinates to the central metal, bridging between macrocycles. An average structure is proposed for this dimer in which the macrocycle planes are parallel, overlap in ring IV and ha

ISSN:0021-2148    

DOI:10.1002/ijch.198100048

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractComparison of the optical, paramagnetic and redox properties of the reduced primary acceptors of Photosystems (PS) I and II with those of chlorophyll and pheophytin anions suggests that chlorophyll is the primary reduced product in PS I and pheophytin in PS II. Molecular orbital calculations provide a description of the electronic profiles of the radicals, and indicate that the protein environment of the chromophores in the reaction center may impose specific orientations and induce hydrogen bonding to some of the chlorophyll substituent groups. Examination of all the primary acceptors postulated for green plants and purple bacteria suggests that (bacterio)chlorophyll‐like acceptors may be obligatory to effect the rapid primary charge separation, because they allow favorable orbital overlap between donor and acceptor. Extrapolation of these results to green bacteria suggests that bacteriochlorophyllaand bacteriopheophytincmay act as transient electron acceptors in these organism

ISSN:0021-2148    

DOI:10.1002/ijch.198100049

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe fluorescence and force‐area behavior of chlorophylla(Chla) monomolecular films diluted with hydrocarbon on an aqueous subphase is reported. It is found that the diluent hexadecane, instead of conventional fatty alcohols, results in a substantial increase in the fluorescence yield of Chla. The luminescence intensity varies nonmonotonically with respect to the intermólecular distance. A model for the mutual orientation of the chlorophyll pigments and the consequent energy transfer processes in terms of a Förster mechanism is proposed. For a random distribution of the Chlamolecules in the monolayer (k2= 2/3) an average value of 43° is calculated for the angle between the molecular planes and the water surface. This model yields a value of 23 Å for the FörsterR0. Also, a value of 58° is derived for the angle between the Q‐band transition moment and the line of intersection between the molecular plane and water surface. When a mixture of Chlaand Chlbin the monolayers is being excited at the absorption band of the latter pigment, typical fluorescence of Chlais being detected. This sensitization process can also be interpreted in terms of the orientational model of the Chl molecules as presented in

ISSN:0021-2148    

DOI:10.1002/ijch.198100050

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractWith an optically detected magnetic resonance technique, Microwave Induced Fluorescence difference (MIF) spectra have been recorded at 1.5 K for a number of photosynthetic bacteria under reducing conditions. It is found that the MIF spectra coincide with the longest wavelength fluorescence band. A relation for energy transfer at very low temperature is derived, leading to a (r0R)−3dependence of the rate of energy transfer on the distancer0of closest approach of donor and acceptor pigment and the diameter 2R of the antenna complex. It is tentatively concluded that the photochemical trap in the photosynthetic reaction center has a distribution of 0‐0 transitions similar to that of the antenna pigme

ISSN:0021-2148    

DOI:10.1002/ijch.198100051

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.198100052

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe addition of 1–50 mM MgCl, to “low salt” thylakoid membranes causes a monotonic decrease in the transverse, aqueous proton relaxation rate (R2= 1/T2) and an increase in the 6‐line ESR spectrum characteristic of free Mn(II) but does not affect the oxygen evolution rate. These results suggest that magnesium ion at low concentrations replaces Mn(II) from a very loosely bound pool which is not involved in oxygen evolution. The decrease ofR2is probably due mainly to the smaller molar relaxivity of free compared with bound Mn(II).R2can be affected by conformational and structural changes involving the Mn(II) as well as by the amount of Mn(II) and the nature of its binding. However, MgCl2causes the same decrease inR2for trypsin treated thylakoids, which do not undergo the gross structural changes, e.g. grana stacking, that it produces in untreated membranes.R2measurements of isolated light harvesting complex preparations indicate the presence of bound Mn in it; neutron activation analysis of these samples shows that they have about one‐third of the functional manganese bound in thylakoid membranes—this may be the tightly bound pool of Mn, but the results are not

ISSN:0021-2148    

DOI:10.1002/ijch.198100053

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY

摘要:

AbstractThe key aggregation steps for C‐phycocyanin consist of denatured subunits (α and β polypeptide chains), monomers, trimers, hexamers and stacks. For allophycocyanin the steps are denatured subunits, monomers and trimers. Ultimately these assembly states lead to the formation of phycobilisomes in blue‐green and red algae. The spectroscopic changes that accompany each stage in the assembly can be monitored as a function of the ratio of visible to near‐UV absorption. For C‐phycocyanin, monomers and hexamers are the important levels in the modulation of tetrapyrrole conformation by protein‐chromophore interaction. The effect of protein aggregation on the protein‐chromophore interactions is the key to solar‐energy harvesting and excitation‐energy migration

ISSN:0021-2148    

DOI:10.1002/ijch.198100054

出版商:WILEY‐VCH Verlag    

年代:1981

数据来源: WILEY