A NEW PATHWAY FOR THE SYNTHESIS OF THE PLANT SULPHOLIPID, SULPHOQUINOVASYLDIACYLGLYCEROL

A new pathway is proposed for the biosynthesis of the plant sulpholipi d, sulphoquinovosyldiacylglycerol. The pathway begins at UDP-glucose a nd involves the formation therefrom of UDP-4-ketoglucose-5-ene to whic h is subsequently added sulphite (or its metabolic equivalent). Eviden ce consistent with this pathway, rather than with the previously propo sed 'sulphoglycolytic' route, was obtained from experiments with pea c hloroplast preparations. The evidence included the failure of potentia l inhibitors of the sulphoglycolytic pathway to alter the rate of synt hesis of sulpholipid and the stimulation of the incorporation of (SO42 -)-S-35 into the latter by UTP. Radioactivity was effectively incorpor ated into sulpholipid from UDP-[C-14]glucose and this radiolabelling w as stimulated by the addition of methyl alpha-glucose-enide or of an e nzyme system known to be forming (although not accumulating) UDP-4-ket oglucose-5-ene. This new pathway is also consistent with other data in the literature.