Biogenesis of yeast sterols. IV. Transmethylation in ergosterol synthesis.

Methionine was found to be more efficient than formate, serine, bicarbonate, formaldehyde, or choline as a source of the C-28 methyl group of ergosterol in yeast (1). While transfer of an intact methyl group to carbon has not been previously recorded, oxidation of the methyl group of methionine to formate has been demonstrated and formate-Cl* has been shown to give rise to C-28 of ergosterol (2). Nevertheless, preliminary experiments in this laboratory indicated that a true transmethylation may occur (3). The experiments described in this paper were designed to elucidate the mechanism of the transfer of the l-carbon unit from methionine to sterol.