DIACYLGLYCEROLS AND PHOSPHATIDATES - WHICH MOLECULAR-SPECIES ARE INTRACELLULAR MESSENGERS

In eukaryotes, many receptor agonists use phospholipase-generated lipi ds as intracellular messengers. Receptor occupation stimulates the pro duction of polyunsaturated 1,2-diacylglycerols by phosphatidylinositol -4,5-bisphosphate-specific phospholipases C and/or of mono-unsaturated and saturated phosphatidates by phospholipase-D-catalysed phosphatidy lcholine breakdown. The primary phospholipase products are rapidly met abolized: polyunsaturated 1,2-diacylglycerols are converted to polyuns aturated phosphatidates by diacylglycerol kinase; mono-unsaturated and saturated phosphatidates are dephosphorylated to give mono-unsaturate d and saturated 1,2-diacylglycerols by phosphatidate phosphohydrolase. The phospholipase-generated polyunsaturated 1,2-diacylglycerols and m ono-unsaturated and saturated phosphatidates appear to be intracellula r messengers, whereas their immediate metabolites probably do not have signalling functions.