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 > phosphatidylglycerol versus phosphatidylglycerol > phosphatidylethanolamine).