On the molecular nature of chloroplast thylakoid membranes

Abstract

Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were disintegrated and the electrophoretic behavior of the components studied with special regard to the pigment-protein complexes. The process of denaturation of the complexes was found to differ with respect to the other protein components. As the result of denaturation, the pigment-free protein moieties exhibit altered electrophoretic mobilities in relation to the intact complexes mainly conditioned by two processes contrary in their action, i.e. increase of change and change of the hydrodynamic properties. Exhaustive extraction of the thylakoid membranes with 6 M guanidine - HCl removes the proteins mainly associated by polar and weak hydrophobic interactions. The insoluble residue quantitatively exhibits the pigment-protein complexes including their denatured protein moieties, two extrinsic hydrophobic proteins as well as some protein traces. Electron-microscopic studies demonstrate the material still to have a high degree of order and preserved basic structure. After removing the lipids from the basic membrane, large amounts of the protein moeity of Complex II become soluble in guanidine -HCl. Since all other lamellar proteins are removable either by quanidine -HCl extraction or by trypsin digestion it is assumed the basic membrane of thylakoid to consist only of the pigment-protein complexes embedded into the lipid matrix.