The relationship of gamone to the mating reaction in Chlamydomonas moewusii

Gamete-gamete adhesion in Chlamydomonas has long been attributed to large glycoprotein particles (gamone) on the flagellar membrane surface. These macromolecules may be incidentally sloughed off or released into the medium. Gamone isolated from the medium of one mating type will cause isoagglutination of opposite gametes. Our study of Chlamydomonas moewusii shows that such particles isolated from the cell medium are really membrane vesicles with mastigonemes (flagellar appendages) attached. The vesicles appear to bleb off the flagellar membrane as a normal process. Purified mastigonemes have no isoagglutinating activity, while purified membrane vesicles (with no mastigonemes attached) retain activity. Therefore, the large particles isolated by others from the cell medium of Chlamydomonas and thought to be equivalent to the gametic adhesion substance are in fact membrane vesicles upon which the adhesion sites are located, and these sites are probably much smaller than was previously supposed. Mastigonemes appear to have no role in gamete adhesion.