Lack of Mammalian Reduction or Alkylation of 24-Methylenecholesterol

The Δ24(28)-bond of 24-methylenecholesterol was not detectably reduced by rats either in vivo or in a liver enzyme preparation. Since the Δ24(25)-bond of other sterols is reduced under the same conditions, mammalian Δ24(25)-reductase must discriminate between the two positions of the pi-electronic system. It also follows that rats do not possess a Δ24(28)-reductase and are therefore incapable of biosynthesizing 24-methylcholesterol as plants do through reduction of a 24-methylene intermediate. 24-Methylenecholesterol also failed in the rat to undergo further addition of a carbon atom to yield a 24-ethylidene- or 24-ethyl derivative as occurs in plants.