The metabolism of the phosphonium analogue of choline in cultured cells. A useful nuclear-magnetic-resonance probe for membrane phosphatidylcholine.

1. Replacement of choline by the phosphonium analogue does not affect the growth rate of P815Y, NIL, 3T3, and SV40/3T3 cells in culture. 2. The fatty acid composition of the resulting phosphonium phosphatidylcholine is similar to that of phosphatidylcholine. 3. The rate of synthesis and degradation of phosphatidylcholine and of the phosphonium analogue are similar. 4. Phospholipid-exchange protein does not distinguish between phosphatidylcholine and the phosphonium analogue. 5. By contrast, incorporation of phosphonium choline into sphingomyelin occurs to only a minor extent. 6. It is concluded that, since the enzymes involved in the turnover of phosphatidylcholine do not discriminate between quaternary N and quaternary P in the polar head-group region, phosphonium choline should prove to be a useful probe for 31P nuclear-magnetic-resonance (n.m.r.) studies of natural membranes.