Methionine metabolism in BHK cells: Selection and characterization of ethionine resistant clones

Abstract

The selection of clones resistant to methionine antagonists was undertaken on baby hamster Kidney cells grown in a methionine free medium, supplemented with homocystine, folic acid and hydroxo-B12. Clones resistant to 30 mug/ml ethionine were isolated after mutagenesis at an induced mutation frequency of 2.3 X 10(-5). An ethionine resistant clone, ETH 304, was extensively studied. The resistant cells excreted methionine in the culture medium and the intracellular pools of methionine and SAM were two to five times greater in the resistant clone than in the wild type cells. A semidominant ethionine resistant phenotype was observed in hybrids between the wild type and this resistant clone. Measurement of the specific activity of menadione reductase, B12 methyltransferase and ATP: L-methionine S-adenosyl-transferase in crude extracts of the wild type showed a repressive action of methionine on the level of the three enzymes. However, the ethionine resistant clone ETH 304 was not modified in this function. Menadione reductase is feedback-inhibited by SAM in wild type cells. The enzyme of the ethionine resistant clone was significantly less sensitive to SAM. When a comparison of thermal stability was made between the wild type and ethionine resistant clone enzymes, it was found that the thermal stability of the latter was modified. Three other ethionine resistant clones, independantly isolated, were similarly affected in the properties of menadione reductase. These results suggest that the pathway of re-use of S-adenosyl homocysteine, produced during methylation reactions, is highly regulated by methionine and SAM.

Methionine Adenosyltransferase ( S ‐Adenosylmethionine Synthetase) and S ‐Adenosylmethionine Decarboxylase

“…6. Methionine adenos yltransferase levels increase in cell cultures grown in methionine-deficient media (99), and decrease upon addition of methionine to the culture media (100,101).…”

Reduced H3K27me3 Suppresses Wnt/β-catenin Signaling by S-adenosylmethionine Deficiency in Neural Tube Development

“…Folate metabolism is essential nutrients required for the two major biological processes, including purine and thymidine monophosphate biosynthesis and methionine regeneration. S-adenosylmethionine (SAM), a key metabolite in the methionine regeneration, acts as a major methyl donor in numerous biochemical reactions [3,4]. It has reported that that abnormalities of SAM were associated with NTDs [5].…”