Intracellular localization of phospholipid transfer activity in Rhodopseudomonas sphaeroides and a possible role in membrane biogenesis

Abstract

The cellular content of phospholipid transfer activity in Rhodopseudomonas sphaeroides was examined as a function of both oxygen partial pressure and light intensity used for growth. Cells grown under high light conditions (100 W/m2) had over two times the cellular level of phospholipid transfer activity when compared with cells grown under other conditions. Although cells grown under low light conditions (3 W/m2) had the lowest amount of total phospholipid transfer activity, they had the highest level (49%) of membrane-associated transfer activity. The soluble phospholipid transfer activity was further localized into periplasmic and cytoplasmic fractions. The distribution of phospholipid transfer activity in cells grown under medium light intensity (10 W/m2) was calculated as 15.1% membrane-associated, 32.4% in the periplasm, and 52.5% in the cytoplasm. The phospholipid transfer activities in the periplasmic and cytoplasmic fractions had distinctly different properties with respect to their molecular weights (56,000 versus 27,000) and specificities of transfer (phosphatidylethanolamine greater than phosphatidylglycerol versus phosphatidylglycerol greater than phosphatidylethanolamine).