AbstractsBiology & Animal Science

Regulation of the terminal reactions for methionine biosynthesis in yeast

by Kemet Dean Spence




Institution: Oregon State University
Department: Microbiology
Degree: PhD
Year: 1965
Keywords: Methionine
Record ID: 1569629
Full text PDF: http://hdl.handle.net/1957/47853


Abstract

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.