INFLUENCE OF PROTONS ON THYLAKOID MEMBRANE STACKING

The effect of protons on thylakoid membranes was examined. On lowering the pH of the suspension medium to pH 5.4 in the presence of a low monovalent cation concentration and in the absence of divalent cations the broken chloroplasts changed from an unstacked to a stacked configuration, identical to that observed at pH 8 in the presence of 5 mM MgCl2. A brief trypsin treatment prevented the thylakoid membranes from forming grana stacks either at pH 8 in the presence of 5 mM MgCl2 or at pH 5.4. These observations indicate that the same protein site(s) is probably involved in membrane stacking caused either by protons or by metal cations at high pH. © 1979.