Insertional Inactivation of the Methionine S-Methyltransferase Gene Eliminates the S-Methylmethionine Cycle and Increases the Methylation Ratio
| Autor: | Stefan Mellema, Michael G. Kocsis, David Rhodes, Mitchell C. Tarczynski, Kazuki Saito, Philippe Ranocha, Eric S. Simon, Conrad Wagner, Changjiang Li, Andrew D. Hanson, Motoko Awazuhara, Robert B. Meeley, Douglas A. Gage, Gregory J. Peel |
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| Rok vydání: | 2003 |
| Předmět: |
S-Adenosylmethionine
Methyltransferase Physiology Mutant Arabidopsis Vitamin U Plant Science 580 Plants (Botany) Biology Methylation Zea mays chemistry.chemical_compound Genetics Sulfhydryl Compounds Methionine S-methyltransferase Amino Acids S-Methylmethionine Methionine Wild type Methyltransferases S-Adenosylhomocysteine Mutagenesis Insertional Biochemistry chemistry Seeds S-methylmethionine cycle Sulfur Research Article |
| Zdroj: | Plant Physiology. 131:1808-1815 |
| ISSN: | 1532-2548 0032-0889 |
| Popis: | Methionine (Met) S-methyltransferase (MMT) catalyzes the synthesis of S-methyl-Met (SMM) from Met andS-adenosyl-Met (Ado-Met). SMM can be reconverted to Met by donating a methyl group to homocysteine (homo-Cys), and concurrent operation of this reaction and that mediated by MMT sets up the SMM cycle. SMM has been hypothesized to be essential as a methyl donor or as a transport form of sulfur, and the SMM cycle has been hypothesized to guard against depletion of the free Met pool by excess Ado-Met synthesis or to regulate Ado-Met level and hence the Ado-Met toS-adenosylhomo-Cys ratio (the methylation ratio). To test these hypotheses, we isolated insertional mmtmutants of Arabidopsis and maize (Zea mays). Both mutants lacked the capacity to produce SMM and thus had no SMM cycle. They nevertheless grew and reproduced normally, and the seeds of the Arabidopsis mutant had normal sulfur contents. These findings rule out an indispensable role for SMM as a methyl donor or in sulfur transport. The Arabidopsis mutant had significantly higher Ado-Met and lowerS-adenosylhomo-Cys levels than the wild type and consequently had a higher methylation ratio (13.8 versus 9.5). Free Met and thiol pools were unaltered in this mutant, although there were moderate decreases (of 30%–60%) in free serine, threonine, proline, and other amino acids. These data indicate that the SMM cycle contributes to regulation of Ado-Met levels rather than preventing depletion of free Met. |
| Databáze: | OpenAIRE |
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