Isolation and characterisation of oxygen evolving thylakoids from the marine prokaryote Prochloron didemni

The present study describes the first successful attempt to isolate oxygen evolving thylakoids and thylakoid fragments from the marine prokaryote Proc hloron didemni, a member of the recently discovered group of prochlorophyte s. Oxygen evolving thylakoid membranes and fragments were isolated from sea water suspended cells of Prochloron didemni by passage of the cells through a Yeda press and subsequent differential centrifugation of the broken mate rial. Three fractions were collected at 1000xg, 5000xg, and 30 000xg and id entified bl light microscopy as cells land their fragments), thylakoids and membrane fragments, respectively. Pigment content, oxygen evolution rate a nd 77 K fluorescence spectra of these fractions were virtually identical. T his finding indicates that the membrane fragments obtained are not enriched in photosystem II. The P680(+.) reduction kinetics of thylakoid membrane f ragments were determined by monitoring flash induced absorption changes at 830 nm and analysing the time course of their decay. The multiphasic relaxa tion kinetics and their modification by NH2OH were found to he similar to t hose observed in cyanobacteria and plants, These findings provide an indepe ndent line of evidence for the idea of a high conservation of the basic str uctural and functional pattern of the water oxidising complex in all organi sms that perform oxygenic photosynthesis. (C) 1999 Federation of European B iochemical Societies.