Lipids of Chlamydomonas reinhardtii. Incorporation of [14C]Acetate, [14C]Palmitate and [14C]Oleate into Different Lipids and Evidence for Lipid-Linked Desaturation of Fatty Acids

摘要

Chlamydomonas reinhardtii, parent strain (ssf), was pulse-labelled with [14C]acetate, [14C]-palmitate or [14C]oleate. Lipids were separated by TLC and HPLC. Radioactivity was measured in each class of lipids and in its fatty acids and molecular species. After 1 hour of incubation with acetate, the label was incorporated mainly into phosphatidylglycerol (PG), diacylglyceryl(N,N,N-trimethyl)homoserine (DGTS), digalactosyldiacylglycerol (DGDG) and monogalactosyldiacylglycerol (MGDG). Saturated, monoene and diene fatty acids were strongly labelled. Within 10 hours of incubation in the absence of labelled precursor, the label shifted from monoenes and dienes to trienes and tetraenes. The transfer of radioactivity from mono- to polyunsaturated MGDG and DGDG molecular species suggests a lipid-linked desaturation of the C-l position (and, in MGDG, also of the C-2 position) of these prokaryotic lipids. In the eukaryotic DGTS, all the species present were labelled simultaneously. On incubation with [14C]-palmitate or [14C]oleate, most of the label appeared in DGTS. Palmitate was immediately incorporated into the polyene species of DGTS, while oleate first appeared in the monoene species and then shifted to the polyene species. From these results it is concluded that, in DGTS, the acyl groups in the C-l position (mostly 16:0) were rapidly exchanged, while those in the C-2 position (mostly C18) became desaturated to give 18:3(5,9,12) and 18:4(5,9,12,15) acids