THE DIHYDROXYACETONEPHOSPHATE PATHWAY FOR BIOSYNTHESIS OF ETHER LIPIDS IN LEISHMANIA-MEXICANA PROMASTIGOTES

Biosynthetic studies using both [C-14]- and [P-32]-labelled substrates and a cell-free system to synthesise 1-O-alkyl moieties in glycerolip ids, have shown that the three initial steps in ether-lipid biosynthes is in Leishmania mexicana promastigotes resemble those described for m ammals and are associated with glycosomes. Purified glycosomes were ab le to sequentially synthesise the first intermediates of the ether-lip id biosynthetic pathway [acyl-dihydroxyacetonephosphate (DHAP), alkyl- DHAP and acyl/alkyl-glycerol-3-phosphate (G3P)] when incubated in the presence of radiolabelled DHAP, palmitoyl-CoA, hexadecanol and NADPH. However, when glycosomes were incubated under the same conditions in t he presence of radiolabelled G3P, a rapid synthesis of acyl-G3P and ph osphatidic acid was observed without any formation of alkyl-G3P, sugge sting that the enzyme alkyl-synthase recognises only acyl-DHAP as subs trate. Both the DHAP acyltransferase (DHAP-AT) and alkyl-DHAP synthase activities were located inside glycosomes whereas the alkyl/acyl-DHAP oxidoreductase activity was associated with the cytoplasmic face of t he glycosomal membrane. The G3P acyltransferase (G3P-AT) and lyso-phos phatidic acid acyltransferase activities were not found inside glycoso mes. The results suggest that the DHAP-AT and G3P-AT activities are ca talysed by two distinct enzymes associated with different sub-cellular compartments. (C) 1997 Elsevier Science B.V.