Phospholipid synthesis in developing flight muscle of Lucilia

Abstract

The synthesis in vivo of microsomal and mitochondrial phospholipids was studied in developing flight muscle of Lucilia cuprina by injecting radioactive phosphate and ethanolamine into insects at various stages of insect development. Incorporation of [32P]phosphate into microsomes and mitochondria is very low on the day immediately prior to emergence, rises markedly 1 day after emergence, especially in the microsomes, and begins to decline at about 2 days postemergence. Prior injection of cycloheximide into newly emerged flies inhibits by about 50 per cent the incorporation of [32P]phosphate into both microsomal and mitochondrial phospholipids. Incorporation of [14C]ethanolamine, like that of [32P]phosphate, was low immediately prior to emergence, increased sharply to a maximum 1 day after emergence, and declined thereafter to reach a minimum at 4 days. Incorporation into the microsomes was much more significant than that into mitochondria. Prior injection of cycloheximide had no effect on the incorporation of [14C]ethanolamine into either cell fraction. [14C]Ethanolamine is incorporated into both mitochondria and microsomes (plus soluble fraction) in vitro in the presence of either Mg2+ or Ca2+. Such incorporation is completely insensitive to CDP-ethanolamine and to phosphorylethanolamine. [32P]Phosphate is incorporated only into the microsomes (plus soluble fraction). It is concluded that incorporation of ethanolamine both in vivo and in vitro into subcellular fractions of Lucilia flight muscle occurs by a process different from that of phosphate and that the synthesis of membrane phospholipids in vivo is closely geared to the synthesis of membrane proteins. Show more