Normal differentiated hepatocytes primarily metabolize methionine, via homocysteine synthesis, through the transsulfuration pathway. In addition to glutathione, this pathway produces α-ketobutyrate that is further metabolized in the mitochondria. It is only under low methionine conditions that differentiated hepatocytes predominantly regenerate methionine from homocysteine. In contrast, prolife...

The transfer of sulfur from methionine to cysteine in the archaebacteria Sulfolobus acidocaldarius and Halobacterium marismortui was studied by feeding 34S-labeled methionine to cells and measuring the incorporation of 34S into protein-bound cellular cysteine and methionine by mass spectrometry. It was found that, as are eucaryotes, both of these archaebacteria were able to convert the sulfur o...

The biochemical properties of two species of methionine transfer ribonucleic acid from bakers’ yeast, separated by diethylaminoethyl Sephadex column chromatography, have been studied. Each species of the two methionine tRNAs, designated methionine tRNA I and methionine tRNA II, respectively, has been purified by benzoylated DEAEcellulose column chromatography. Methionine tRNA I can be esterifie...

Hartley (4) has reported the amino acid sequence of a 25-residue peptide from the tryptic digest of X-sulfochymotrypsinogen which contains the “active center” serine as well as both methionine residues of a-chymotrypsin (Fig. 1). By kinetic analysis, Ray et al. (5, 6) deduced that 1 of the 2 methionine residues and 1 of the 2 histidine residues in chymotrypsin are rapidly destroyed on photo-oxi...

A large proportion of human tumor-derived cell lines and primary tumor cells show methionine-dependent growth. This phenomenon refers to the ability of cells to grow in media containing methionine and the inability of cells to grow in media supplemented with methionine's precursor, homocysteine (Hcy). Methionine can be formed by two different pathways, the recycling pathway and the salvage path...

Reactive oxygen intermediates generated by neutrophils kill bacteria and are implicated in inflammatory tissue injury, but precise molecular targets are undefined. We demonstrate that neutrophils use myeloperoxidase (MPO) to convert methionine residues of ingested Escherichia coli to methionine sulfoxide in high yield. Neutrophils deficient in individual components of the MPO system (MPO, H(2)O...