STEREOCHEMISTRY OF HYDROGEN MIGRATION FROM C-24 TO C-25 DURING BIOMETHYLATION IN ERGOSTEROL BIOSYNTHESIS

[methyl-H-2(3)]Methionine and zymosterol, [27-C-13]lanosterol, [24-H-2 ]lanosterol and lanosterol were separately incubated with the sterol a uxotroph Saccharomyces cerevisiae strain GL7. Spectral evidence (H-1 a nd C-13-NMR) obtained on three different isotopically labeled ergoster ol samples indicated that C-28 was derived from AdoMet, H-24 migrated to C-25 and the C-25 hydrogen on (27-)-methyl C-13-labeled ergosterol was introduced from the Re -face to produce the 25R-stereochemistry.