Les stérols et leurs précurseurs chez Astasia longa Pringsheim

Sterols and sterol precursors of Astasia longa were characterised by thin‐layer chromatography, gas chromatography and mass spectrometry. Sterols were found in liposoluble fractions in the form of free alcohols, esters or glycosides, in hydrosoluble fractions and in the culture medium in the form of free alcohols and esters. Triterpenes and 4α‐methyl sterols were encountered only in the form of free alcohols in both liposoluble and hydrosoluble fractions of the cell. The following compounds have been found in cell cultures: cycloartenol, 24‐methylene‐cycloartanol, cycloeucalenol, obtusifoliol, 4α‐methyl‐Δ8‐ergostenol, Δ7‐cholestenol, cholesterol, Δ7‐ergostenol, Δ5‐ergostenol, isofucosterol, Δ7‐chondrillastenol, clionasterol and poriferasterol. In one culture, some new compounds were accumulated for unknown reasons: 4α,14α‐di‐methyl‐(24S)‐Δ8,25(26)‐stigmastadienol, 14α‐methyl‐(24S)‐Δ8,25(26)‐stigmastadienol, 24‐methylene pollinastanol and 24‐methylpollinastanol. The sterol composition of Astasia longa is consistent with the hypothesis that this alga is a natural mutant of Euglena which has lost all potential for photosynthesis. The presence of cycloartenol and its metabolites shows that in this nonphotosynthesizing organism sterol biosynthesis follows a plant‐type pathway. It is also suggested that several biosynthetic pathways coexist and are expressed differently depending upon the physiological condition of the alga.