[Phosphatidyl glycerol antiserum and its reactions with chloroplasts].

By immunisation of rabbits with stroma-freed chloroplasts and other preparations of the lamellar system, antibodies to phosphatidyl glycerol were formed. By injection of phosphatidyl glycerol, bound to methylated bovine serum albumin, the rabbits also reacted with the formation of antibodies to this phosphatide. The antiserum to phosphatidyl glycerol yielded no reactions with phosphatidyl choline and the glycolipids sulphoquinovosyl diglyceride and mono- and digalactosyl diglyceride, which are present in chloroplasts. Stroma-freed chloroplasts from Antirrhinum majus and Nicotiana tabacum were not agglutinated by antisera to phosphatidyl glycerol. By means of the Coombs test, the “mixed-antigen-agglutination” and sateration experiments it was possible to demonstrate that antibodies to phosphatidyl glycerol are specifically adsorbed onto stroma-freed chloroplasts. After partial protein decomposition by proteases, stroma-freed chloroplasts were agglutinated. Fragments of the thylakoid membranes (ultrasonic supernatant) were precipitated only after partial protein decomposition and functioned in the Coombs test just like stroma-freed chloroplasts. However, fragments of the lamellar system (ultrasonic sediment) were directly agglutinated. Isolated chloroplasts in tris buffer-sucrose solution and in tris buffer-sodium chloride solution were equally agglutinated by antiserum to phosphatidyl glycerol. From the experiments it is concluded that the antigen determinants of the phosphatidyl glycerol are located on the antibody-accessible surface of the thylakoids. The agglutination of stroma-freed chloroplasts was, however, sterically hindered by membrane proteins. In those cases in which chloroplast preparations were directly agglutinated, it is assumed that either thylakoids were disrupted or that they were swollen, resulting in a change in the protein layer of the membranes in such a way that no steric hindrance occurs.