PubMed:10801789 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PubMed/sourceid/10801789","sourcedb":"PubMed","sourceid":"10801789","source_url":"http://www.ncbi.nlm.nih.gov/pubmed/10801789","text":"Recruitment of a foreign quinone into the A1 site of photosystem I. Altered kinetics of electron transfer in phylloquinone biosynthetic pathway mutants studied by time-resolved optical, EPR, and electrometric techniques.\nInterruption of the menA or menB gene in Synechocystis sp. PCC 6803 results in the incorporation of a foreign quinone, termed Q, into the A(1) site of photosystem I with a number of experimental indicators identifying Q as plastoquinone-9. A global multiexponential analysis of time-resolved optical spectra in the blue region shows the following three kinetic components: 1) a 3-ms lifetime in the absence of methyl viologen that represents charge recombination between P700(+) and an FeS(-) cluster; 2) a 750-microseconds lifetime that represents electron donation from an FeS(-) cluster to methyl viologen; and 3) an approximately 15-microseconds lifetime that represents an electrochromic shift of a carotenoid pigment. Room temperature direct detection transient EPR studies of forward electron transfer show a spectrum of P700(+) Q(-) during the lifetime of the spin polarization and give no evidence of a significant population of P700(+) FeS(-) for t \u003c/= 2-3 microseconds. The UV difference spectrum measured 5 microseconds after a flash shows a maximum at 315 nm, a crossover at 280 nm, and a minimum at 255 nm as well as a shoulder at 290-295 nm, all of which are characteristic of the plastoquinone-9 anion radical. Kinetic measurements that monitor Q at 315 nm show a major phase of forward electron transfer to the FeS clusters with a lifetime of approximately 15 microseconds, which matches the electrochromic shift at 485 nm of the carotenoid, as well as an minor phase with a lifetime of approximately 250 microseconds. Electrometric measurements show similar biphasic kinetics. The slower kinetic phase can be detected using time-resolved EPR spectroscopy and has a spectrum characteristic of a semiquinone anion radical. We estimate the redox potential of plastoquinone-9 in the A(1) site to be more oxidizing than phylloquinone so that electron transfer from Q(-) to F(X) is thermodynamically unfavorable in the menA and menB mutants.","tracks":[{"project":"sentences","denotations":[{"id":"T1","span":{"begin":0,"end":67},"obj":"Sentence"},{"id":"T2","span":{"begin":68,"end":220},"obj":"Sentence"},{"id":"T3","span":{"begin":221,"end":279},"obj":"Sentence"},{"id":"T4","span":{"begin":280,"end":460},"obj":"Sentence"},{"id":"T5","span":{"begin":461,"end":593},"obj":"Sentence"},{"id":"T6","span":{"begin":594,"end":944},"obj":"Sentence"},{"id":"T7","span":{"begin":945,"end":1201},"obj":"Sentence"},{"id":"T8","span":{"begin":1202,"end":1447},"obj":"Sentence"},{"id":"T9","span":{"begin":1448,"end":1756},"obj":"Sentence"},{"id":"T10","span":{"begin":1757,"end":1815},"obj":"Sentence"},{"id":"T11","span":{"begin":1816,"end":1959},"obj":"Sentence"},{"id":"T12","span":{"begin":1960,"end":2174},"obj":"Sentence"}],"namespaces":[{"prefix":"_base","uri":"http://pubannotation.org/ontology/tao.owl#"}],"attributes":[{"subj":"T1","pred":"source","obj":"sentences"},{"subj":"T2","pred":"source","obj":"sentences"},{"subj":"T3","pred":"source","obj":"sentences"},{"subj":"T4","pred":"source","obj":"sentences"},{"subj":"T5","pred":"source","obj":"sentences"},{"subj":"T6","pred":"source","obj":"sentences"},{"subj":"T7","pred":"source","obj":"sentences"},{"subj":"T8","pred":"source","obj":"sentences"},{"subj":"T9","pred":"source","obj":"sentences"},{"subj":"T10","pred":"source","obj":"sentences"},{"subj":"T11","pred":"source","obj":"sentences"},{"subj":"T12","pred":"source","obj":"sentences"}]},{"project":"Glycosmos6-MAT","denotations":[{"id":"T1","span":{"begin":936,"end":943},"obj":"http://purl.obolibrary.org/obo/MAT_0000159"}],"attributes":[{"subj":"T1","pred":"source","obj":"Glycosmos6-MAT"}]},{"project":"CyanoBase","denotations":[{"id":"T1","span":{"begin":249,"end":253},"obj":"protein"},{"id":"T2","span":{"begin":2161,"end":2165},"obj":"protein"}],"attributes":[{"subj":"T1","pred":"source","obj":"CyanoBase"},{"subj":"T2","pred":"source","obj":"CyanoBase"}]},{"project":"mondo_disease","denotations":[{"id":"T1","span":{"begin":280,"end":283},"obj":"Disease"}],"attributes":[{"id":"A1","pred":"mondo_id","subj":"T1","obj":"http://purl.obolibrary.org/obo/MONDO_0004974"},{"id":"A2","pred":"mondo_id","subj":"T1","obj":"http://purl.obolibrary.org/obo/MONDO_0022673"},{"subj":"T1","pred":"source","obj":"mondo_disease"}]},{"project":"NCBITAXON","denotations":[{"id":"T1","span":{"begin":262,"end":275},"obj":"OrganismTaxon"}],"attributes":[{"id":"A1","pred":"db_id","subj":"T1","obj":"1142"},{"subj":"T1","pred":"source","obj":"NCBITAXON"}]},{"project":"Anatomy-UBERON","denotations":[{"id":"T1","span":{"begin":1354,"end":1362},"obj":"Body_part"}],"attributes":[{"id":"A1","pred":"uberon_id","subj":"T1","obj":"http://purl.obolibrary.org/obo/UBERON_0001467"},{"subj":"T1","pred":"source","obj":"Anatomy-UBERON"}]},{"project":"Anatomy-MAT","denotations":[{"id":"T1","span":{"begin":936,"end":943},"obj":"Body_part"}],"attributes":[{"id":"A1","pred":"mat_id","subj":"T1","obj":"http://purl.obolibrary.org/obo/MAT_0000159"},{"subj":"T1","pred":"source","obj":"Anatomy-MAT"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"sentences","color":"#ec93af","default":true},{"id":"Glycosmos6-MAT","color":"#93c9ec"},{"id":"CyanoBase","color":"#e3ec93"},{"id":"mondo_disease","color":"#da93ec"},{"id":"NCBITAXON","color":"#93ecc0"},{"id":"Anatomy-UBERON","color":"#eca693"},{"id":"Anatomy-MAT","color":"#9399ec"}]}]}}