Regulation of the terminal reactions for methionine biosynthesis in yeast
Institution: | Oregon State University |
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Department: | Microbiology |
Degree: | PhD |
Year: | 1965 |
Keywords: | Methionine |
Record ID: | 1569629 |
Full text PDF: | http://hdl.handle.net/1957/47853 |
Studies were carried out to elucidate the mechanism of enzymatic control of methionine biosynthesis in Saccharomyces cerevisiae. Enzymatic studies demonstrated that, in addition to the methionine activating enzyme, the S-adenosylmethionine:homocysteine transmethylase enzyme was induced during cultivation in the presence of excess methionine. A similar, though reduced effect was observed when homocysteine and serine were present in the medium. The serine hydroxymethylase enzyme was repressed under these conditions. Ethionine-resistant mutants were isolated to facilitate these studies. These organisms were shown to possess a reduced ability for converting methionine to S-adenosylmethionine. These organisms accumulated more intracellular methionine than the wild-type strain. The mutants were also found to excrete more methionine into the medium than the parental strain. All mutants tested showed a reduced level of the transmethylase enzyme. Two showed a reduced level of the methionine activating enzyme. Studies which measured the accumulation and intracellular distribution of ethionine (ethyl-C¹⁴) and methionine (methyl-C¹⁴) were also carried out. The mutants were able to exclude' the analog from participation in most cellular processes.