Biosynthesis of 24-methylcholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol inZea mays.

The relative rates of synthesis of 24-methylcholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol inZea mays shoots were determined using [2-(14)C]mevalonic acid and [methyl-(14)C]methionine as substrates. The 24-ethylsterol had a higher specific activity and it apparently was synthesized at about 3-4 times the rate of the 24-methylsterol.(1)H NMR spectroscopy showed that the 24-ethylsterol was predominantly the 24α-epimer but the 24-methylsterol was a mixture of the 24α-epimer (30-40%) and the 24β-epimer (60-70%). The results are discussed in relation to the involvement of Δ(24(28))-, Δ(23), Δ(25)- and Δ(24(25))-sterol intermediates in 24-methyl- and 24-ethylsterol production.