ON SEXUAL AGGLUTINATION AND MATING-TYPE SUBSTANCES IN ISOGAMOUS DIOECIOUS CHLAMYDOMONADS. III. THE SENSITIVITY OF SEX CELL CONTACT TO VARIOUS ENZYMES'

The components responsible for sex cell contact in dioecious Chlamydomnonas species have been characterized by their sensitivity to enzymes. The mating-type substances, which are glycoprotein complexes according to the analysis of the corresponding isoagglutinins, were incubated with proteases, glycosidases, and with sulfatase. An enzyme may or may not affect both gamete types of a species or it may discriminate between the sexes, eliminating one mating-type activity only. In no case was an incapacitation of a given gamete type based upon the detachment of the proper contact component as an isoagglutinin or as a functionally univalent structure with a specific receptor-blocking power against the complementary type. Inactivating enzymes seem to interfere with the surface configuration essential for gamete contact or to eliminate actual contact sites. The compilation of data for six taxa reveals a complex sensitivity pattem of the gametes' agglutinability. Two types of interactions appear to occur. In C. reinhardti and C. chlamydogama the contact mechanism seems to depend on an interaction between two proteinaceous structures. In C. eugametos and C. moewusii definite proof was obtained for a contact based upon a carbohydrate-protein interaction. In the (+) sexes of C. eugametos and C. moewusii syngen 11, a-glycosidically bound terminal mannose residues are essential for the contact. Neither ,-galactosidase, neuraminidase, or sulfatase incapacitate the mating-type substances in situ. THE MOLECULAR BASIS and mechanism of sex cell contact were studied in the mating-type reaction of isogamous dioecious Chlamydomonas species. This surface-to-surface interaction initiating copulation is based upon sex- and speciesspecific components at the flagella tips, the matingtype substances. Components with the specific contact capacity of the mating-type substances have been isolated from the supernate of gametes.