FIGURE 1.

Metabolism of Met and Met sulfoxide in mammalian cells. Protein synthesis and methylation and trans-sulfuration pathways represent major uses of free Met. The current study adds information on an additional Met cycle wherein Met is oxidized to Met-RO and Met-SO, and only Met-SO can be reduced to Met. Expression of yeast fRMsr allows utilization of Met-RO, compensating for deficiency in this function in mammals. MAT, methionine adenosyltransferase; SAM, S-adenosylmethionine; SAH, S-adenosylhomocysteine; SAHH, S-adenosylhomocysteine hydrolase; CGL, cystathionine γ-lyase; MS, methionine synthase; THF, tetrahydrofolate; DMG, dimethyl glycine; BHMT, betaine:homocysteine methyltransferase.