Figure 3.

Ergosterol chemical structure is shown illustrating the C22-desaturation undertaken by CYP61/CYP710. For comparison, the molecular structures of cholesterol and a phytosterol, stigmasterol, are also given. Inset is a micrograph of the filipin-stained unicellular choanoflagellate Monosiga ovate (filipin binds to ergosterol). The presence of ergosterol in the closest living relatives of metazoans and as the most common end product in protists, fungi and some algae, suggests the evolution of ergosterol was most likely an early event in eukaryote evolution, or was repeatedly gained over time.