| Cellular levels of glutamyl-tRNA reductase and glutamate-1-semialdehyde aminotransferase do not control chlorophyll synthesis in Chlamydomonas reinhardtii. | |
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MedLine Citation:
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PMID: 16126849 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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5-Aminolevulinic acid (ALA) is the first committed universal precursor in the tetrapyrrole biosynthesis pathway. In plants, algae, and most bacteria, ALA is generated from glutamate. First, glutamyl-tRNA synthetase activates glutamate by ligating it to tRNA(Glu). Activated glutamate is then converted to glutamate 1-semialdehyde (GSA) by glutamyl-tRNA reductase (GTR). Finally, GSA is rearranged to ALA by GSA aminotransferase (GSAT). In the unicellular green alga Chlamydomonas reinhardtii, GTR and GSAT were found in the chloroplasts and were not detected in the mitochondria by immunoblotting. The levels of both proteins (assayed by immunoblotting) and their mRNAs (assayed by RNA blotting) were approximately equally abundant in cells growing in continuous dark or continuous light (fluorescent tubes, 80 micromol photons s(-1) m(-2)), consistent with the ability of the cells to form chlorophyll under both conditions. In cells synchronized to a 12-h-light/12-h-dark cycle, chlorophyll accumulated only during the light phase. However, GTR and GSAT were present at all phases of the cycle. The GTR mRNA level increased in the light and peaked about 2-fold at 2 h into the light phase, and GTR protein levels also increased and peaked 2-fold at 4 to 6 h into the light phase. In contrast, although the GSAT mRNA level increased severalfold at 2 h into the light phase, the level of GSAT protein remained approximately constant in the light and dark phases. Under all growth conditions, the cells contained significantly more GSAT than GTR on a molar basis. Our results indicate that the rate of chlorophyll synthesis in C. reinhardtii is not directly controlled by the expression levels of the mRNAs for GTR or GSAT, or by the cellular abundance of these enzyme proteins. |
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Authors:
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Luiza A Nogaj; Alaka Srivastava; Robert van Lis; Samuel I Beale |
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Publication Detail:
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Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S. Date: 2005-08-26 |
Journal Detail:
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Title: Plant physiology Volume: 139 ISSN: 0032-0889 ISO Abbreviation: Plant Physiol. Publication Date: 2005 Sep |
Date Detail:
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Created Date: 2005-09-16 Completed Date: 2006-01-23 Revised Date: 2010-09-21 |
Medline Journal Info:
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Nlm Unique ID: 0401224 Medline TA: Plant Physiol Country: United States |
Other Details:
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Languages: eng Pagination: 389-96 Citation Subset: IM |
Affiliation:
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Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Aldehyde Oxidoreductases
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genetics,
immunology,
metabolism* Animals Chlamydomonas reinhardtii / enzymology, metabolism*, radiation effects Chlorophyll / biosynthesis* Darkness Gene Expression Regulation, Enzymologic Intramolecular Transferases / genetics, immunology, metabolism* Light Protein Transport RNA, Messenger / genetics, metabolism |
| Chemical | |
Reg. No./Substance:
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0/RNA, Messenger; 1406-65-1/Chlorophyll; EC 1.2.-/Aldehyde Oxidoreductases; EC 1.2.1.-/glutamyl tRNA reductase; EC 5.4.-/Intramolecular Transferases; EC 5.4.3.8/glutamate-1-semialdehyde 2,1-aminomutase |
| Comments/Corrections | |
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