In Vitro Biosynthesis of the Plant Sulpholipid: On the Origin of the Sulphonate Group

Biosynthesis of the plant sulpholipid (diacylsulphoquinovosyl glycerol) has been demonstrated in a cell-free assay system from the green alga Chlamydomonas reinhardii CW 15. The sulpholipid was labelled with [35S]sulphate when ATP, Mg2+ and a reductant were provided. Unlabelied cysteic acid failed to suppress the labelling of the sulphonate group in the lipid. Labelling with [35S]PAPS or [35S]sulphite has been studied in a fractionated cell extract. Sulphite as a precursor only required a particulate fraction of the cell while with PAPS the assay had to be complemented with a soluble protein and a thiol compound. [35S]PAPS was incorporated into the diacylsulphoquinovosyl glycerol with a higher specificity than sulphite.