FORMATION AND MATURATION OF PHAGOSOMES LABELED BY MAGNETIC MICRO PARTICLES - AN ULTRASTRUCTURAL-STUDY IN TETRAHYMENA-THERMOPHILA

Phagosomes of Tetrahymena thermophila were pulse-chase labeled with co lloidal magnetic iron-starch particles. These labeled phagosomes are e asily purified by magnets in large quantities. They allow us to analys e their biochemical composition which is expected to change stage-spec ifically during their maturation. Although preliminary observations ha d shown that these phagosomes are processed similar to phagosomes labe led with food bacteria, we decided to prove the observations at the ul trastructural level. In addition we used phagosomes isolated at define d stages of maturation to study the distribution and number of the int ramembrane particles by freeze-fracturing. As no significant differenc es in processing of phagosomes labeled with bacteria or iron-starch pa rticles were observed, the biochemical data obtained from analysis of magnetically isolated phagosomes will most probably correspond to thei r authentic composition.