Inhibition and substrate specificity of yeast Δ²²-desanturase

Using yeast microsomes, 23-hydroxysterols were tested as intermediates in the formation of the sterol side Δ²²-double bond. No evidence could be found supporting a two-stage mechamism of desaturation via hydroxylation and dehydration. Sterols with various side chains were tested as substrates. Those with alkyl substituents in the 24-α position were poor substrates. A series of sterols, including cyclopropyl sterols, were tested as mechanism-based inhibitors without success. Inhibition was observed with an isocyano-sterol.