The terminal reaction in the formation of methionine from serine or formaldehyde has been studied in a cell-free system derived from bovine brain. The enzyme responsible for this reaction, N^5-methyltetra-hydrofolate:homocysteine transmethylase, catalyzes the conversion of homocysteine to methionine by the transfer of the N^5-methyl group of N^5-methyltetrahydrofolate to homocysteine. The conversion requires a reducing system such as a reduced flavin, and cofactors adenosine triphosphate and Mg^++, or S-adenosylmethionine. The enzyme is one of two in the mammalian system known for its dependence on vitamin B_12. A 374-fold purification of the transmethylase has been achieved by protamine sulfate and ammonium sulfate fractionations followed by various column chromatography procedures. The partially purified transmethylase exhibits absorption maxima at 343, 405, and 472 mu with a broad band extending from 508 to 566 mu. These peaks are due to a form of vitamin B_12 bound to the transmethylase. The enzyme exhibits a pH optimum at 6.8 and a temperature optimum at 45°.
| Identifer | oai:union.ndltd.org:BGMYU2/oai:scholarsarchive.byu.edu:etd-9360 |
| Date | 01 August 1970 |
| Creators | Steuart, Bradley William |
| Publisher | BYU ScholarsArchive |
| Source Sets | Brigham Young University |
| Detected Language | English |
| Type | text |
| Source | Theses and Dissertations |
| Rights | http://lib.byu.edu/about/copyright/ |
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