Effects of Lipase and Phospholipase-Treatments on PSII: Differences Between Thermophilic Cyanobacterial and Higher Plant PSII

Abstract

Lipids Constituent One Of The Important Components Of Membrane Protein Complexes, And 14 Lipid Molecules Have Been Identified In The Crystal Structure Of Photosystem Ii (Psii) From A Thermophilic Cyanobacterium Thermosynechococcus Elongatus. In Order To Study The Roles Of Lipids In Psii, We Treated Psii Dimer Complexes From Cyanobacteria And Higher Plants With A Lipase And A Phospholipase A₂ (Pla₂), And Compared Their Effects On Psii Activity And Organization. Lipaseand Pla₂-Treatments Of Psii Dimer From Spinach Decreased The Oxygen-Evolving Activity By 6575% In Both Cases, Whereas The Same Treatments Of Psii Dimer From A Thermophilic Cyanobacterium T. Vulcanus Decreased The Activity By 16% And 40%, Respectively. These Results Suggested That The Association Of Lipids With Spinach Psii Is Significantly Weaker Than That With The Thermophilic Cyanobacterial Psii, Leading To The Significantly Larger Decrease Of Activity After Either Lipase Or Phospholipase- Treatments In Spinach Psii. The Differences In Lipid Binding Observed Here May Account For, At Least In Part, The Significantly Larger Instability Of The Spinach Psii Compared With The Thermophilic Cyanobacterial Psii As Usually Observed.