Using immunological techniques we tried to determine the localization and orientation of the sulpholipid of diloroplasts in thylakoids. During immunization of rabbits with lamellar systems of chloroplasts of Antirrhinum majus antisera were obtained which precipitated sulpholipid emulsions. Antibodies against the sulpholipid were not detected until a second series of intravenous injections.
By immunizing purified sulpholipid of Fucus serratus, adsorbed to methylated bovine serum albumin, sulpholipid antisera were acquired. These antisera and the antisera against lamellar systems of Antirrhinum majus reacted with preparations of sulpholipid from widely different plant species. The sulpholipid antisera did not react with emulsions of the mono- or digalactosyl-diacyl glycerol, of lecithin or the anionic phosphatide phosphatidyl glycerol. Lamellar systems isolated without osmotic shock on a sucrose gradient were not agglutinated by sulpholipid antisera directly, but an indirect agglutination could be achieved in a Coombs-test or in a mixed antigen agglutination after Uhlenbruck. Broken chloroplasts, however, were agglutinated directly by sulpholipid antisera, as well lamellar systems which had been disrupted in a French-press or by ultrasonic treatment.
From agglutination and agglutination inhibition experiments with lamellar systems prepared by different methods it is concluded that the determinant groups of the sulpholipid are accessible for antibodies in the lamellar system of chloroplasts. But probably the sulpholipid molecules are located inside the thylakoids.