Taurine conjugates in the lipid fraction of Euglena cells and their mitochondria

Abstract

Dark-grown resting (non-dividing) cells of Euglena gracilis var. bacillaris and mutants W3BUL (with a proplastid remnant) and W10BSmL (lacking plastids) incubated with 35SO42- form a series of labelled lipids which are low or absent in dividing cells. These lipids all release labelled taurine on mild acid-hydrolysis. Treatment of the labelled lipids with 2,4-dinitrofluorobenzene (DNFB) followed by acid hydrolysis does not yield labelled dinitrophenyltaurine (DNP-taurine), but treatment with DNFB after hydrolysis readily forms labelled DNP-taurine, indicating that taurine is linked to the lipids by at least the amino group. Illumination increases the labelling of these taurolipids in plastid-containing cells (wild-type and W3BUL) but has little effect in cells lacking plastids (W10BSmL); labelling is highest in W10 cells irrespective of illumination. This indicates that the presence of a plastid may exert a negative control on taurolipid formation which is relieved by light. The same series of labelled lipids is found in isolated purified mitochondria from mutant W10, indicating that this organelle is a site for taurolipid deposition. The formation of taurolipids under non-dividing conditions may be a response to nutritional stress and these negatively charged constituents (as well as the thylakoid sulpholipid) may serve to protect membranes by repelling deleterious negatively charged oxygen species.