chlorophyll-a and 9-10-anthraquinone

A photosystem I (PS I) complex containing plastoquinone-9 (PQ-9) but devoid of F(X), F(B), and F(A) was isolated and characterized from a mutant strain of Synechococcus sp. PCC 7002 in which the menB and rubA genes were insertionally inactivated. In isolated PS I trimers, the decay of P700+ measured in the near-IR and the decay of A1- measured in the near-UV were found to be biphasic, with (averaged) room temperature lifetimes of 12 and 350 micros. The decay-associated spectra of both kinetic phases are characteristic of the oxidized minus reduced difference spectrum of a semiquinone, consistent with charge recombination between P700+ and PQ-9-. The amplitude of the flash-induced absorbance changes in both the near-IR and the near-UV show that approximately one-half of the A1 binding sites are either empty or nonfunctional. A spin-polarized chlorophyll triplet is observed by time-resolved EPR, and it is attributed to the 3P700 product of P700+A0- charge recombination via the T0 spin level in those PS I complexes that do not contain a functional quinone. In those A1 sites that are occupied, the P700+Q- polarization pattern indicates that PQ-9 is oriented in a similar manner to that in the menB mutant. When excess 9,10-anthraquinone is added in vitro, it displaces PQ-9 and occupies the A1 binding site more readily than in the menB mutant. This can be explained by a greater accessibility to the A1 site in the menB rubA mutant due to the absence of F(X) and the stromal ridge polypeptides. The relatively low binding affinity of 9,10-anthraquinone allows it to be readily removed from the A1 site by washing. However, all A1 sites are shown to bind napthoquinones with high affinity and thus are proven to be functionally competent in quinone binding. The ability to readily displace PQ-9 from the A1 site makes the menB rubA mutant ideal for introducing novel quinones, particularly anthraquinones, into PS I.

Topics: Anthraquinones; Binding Sites; Chlorophyll; Chromatography, High Pressure Liquid; Dimerization; DNA Restriction Enzymes; Electron Spin Resonance Spectroscopy; Electron Transport; Flavodoxin; Iron-Sulfur Proteins; Kinetics; Models, Genetic; Mutation; Oxidation-Reduction; Peptides; Photosystem I Protein Complex; Plastoquinone; Quinones; Spectrophotometry, Infrared; Synechococcus; Temperature; Time Factors; Ultraviolet Rays

Musty "off-flavor" in pond-cultured channel catfish (Ictalurus punctatus) costs the catfish production industry in the United States at least 30 million US dollars annually. The cyanobacterium Oscillatoria perornata (Skuja) is credited with being the major cause of musty off-flavor in farm-raised catfish in Mississippi. The herbicides diuron and copper sulfate, currently used by catfish producers as algicides to help mitigate musty off-flavor problems, have several drawbacks, including broad-spectrum toxicity towards the entire phytoplankton community that can lead to water quality deterioration and subsequent fish death. By use of microtiter plate bioassays, a novel group of compounds derived from the natural compound 9,10-anthraquinone have been found to be much more selectively toxic towards O. perornata than diuron and copper sulfate. In efficacy studies using limnocorrals placed in catfish production ponds, application rates of 0.3 micro M (125 micro g/liter) of the most promising anthraquinone derivative, 2-[methylamino-N-(1'-methylethyl)]-9,10-anthraquinone monophosphate (anthraquinone-59), dramatically reduced the abundance of O. perornata and levels of 2-methylisoborneol, the musty compound produced by O. perornata. The abundance of green algae and diatoms increased dramatically 2 days after application of a 0.3 micro M concentration of anthraquinone-59 to pond water within the limnocorrals. The half-life of anthraquinone-59 in pond water was determined to be 19 h, making it much less persistent than diuron. Anthraquinone-59 appears to be promising for use as a selective algicide in catfish aquaculture.

Topics: Animals; Anthraquinones; Chlorophyll; Chlorophyll A; Chromatography, High Pressure Liquid; Copper Sulfate; Cyanobacteria; Diuron; Ictaluridae; Kinetics; Naphthols; Odorants; Reproducibility of Results; Water

As analogs of the Photosystem II plastoquinone electron acceptor, QB, substituted quinones compete with QB for a common binding domain and thereby inhibit QB function. Substituted quinones interact with the QB binding niche via hydrogen bonds, and the extent of hydrogen bond formation is determined by quinone structure. We have previously shown that the quinone inhibitory activity can be quantitated using measurements of chlorophyll fluorescence quenching. To assess competition for the QB binding site, we report here measurements of the action of various pairs of substituted anthraquinones on the chlorophyll fluorescence emission of barley chloroplasts. The degree of competition between quinones for the QB binding site is classified as competition, partial competition, or no competition. Two quinones were classified as undergoing competition, i.e., interacting for the same or overlapping sites, if the chlorophyll fluorescence level in the presence of the two quinones was not as low as that achieved in the presence of either one of the quinones individually. Non-competitive quinones with different binding sites quenched chlorophyll fluorescence to the level expected if the quenching effects of the individual quinones were additive. Partial competition, or some interaction for the same or overlapping sites, was characterized by an extent of fluorescence quenching in the presence of two quinones that was more effective than either quinone alone but not as sizable as that expected when the two quinones act independently. These results reflect an interesting situation whereby substitution patterns can alter the binding characteristics within a single class of inhibitors. In an accompanying manuscript we report the results of CNDO molecular orbital calculations to demonstrate that the pi charge distribution in substituted quinones governs their binding properties.

Topics: Anthraquinones; Binding, Competitive; Chlorophyll; Chloroplasts; Fluorescence; Hordeum; Light-Harvesting Protein Complexes; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex

In the accompanying paper (Biochim. Biophys. Acta (1990) 1020, 163-168), we have determined the degree of competition between substituted 9,10-anthraquinones for the QB binding niche through measurements of the additivity of quinone-quenching effects on chlorophyll fluorescence. Quinones inhibit QB function by competitively displacing QB through hydrogen-bond formation with the QB binding protein. The sign of the net pi-charge density on atoms adjacent to the carbonyl moieties is believed to determine the particular hydrogen-bond(s) that result(s). In this study we report CNDO molecular orbital calculations of pi electronic charge distribution in substituted 9,10-anthraquinones to explore the relationship of inhibitor activity and competition to sign of net pi-charge density. We find that the substitution patterns of 9,10-anthraquinones alter the signs of the net pi-charge densities on the carbon atoms adjacent to the carbonyl moieties and thus determine the binding properties of the anthraquinones in the QB niche. While most experimentally studied 9,10-anthraquinones use both carbonyl oxygens to hydrogen bond to the histidine-215 and serine-264 regions of the D-1 QB binding protein, some quinones appear to hydrogen-bond to only one site. Thus, 9,10-anthraquinones constitute a class of QB inhibitors that function as either members of the histidine or serine family of QB inhibitors or as simultaneous representatives of both inhibitor groups.

Topics: Anthraquinones; Binding, Competitive; Chlorophyll; Electrons; Hydrogen Bonding; Light-Harvesting Protein Complexes; Photosynthetic Reaction Center Complex Proteins