Inhibition of Pair Formation by Concanavalin A and Concanavalin A-Binding Glycoconjugates in Euplotes octocarinatus

ABSTRACT. Concanavalin A (≥ 50 μg/ml) inhibits pair formation in both of the two complementary mating types of Euplotes octocarinatus studied in this investigation. This effect can be reversed by methyl-α- d -mannose. Concanavalin A is accessible for methyl-α- d -mannose until pairs are formed. Methyl-α- d -mannose as well as methyl-α- d -glucose and 2-acetamido-2-deoxy- d -glucose alone do not inhibit pair formation unless applied in concentrations ≥ 60 mM. The Concanavalin A-sensitive phase of preconjugant interaction starts 2 h after cells are induced to conjugate. Based on these observations we suggest that Concanavalin A might exhibit its action by binding to carbohydrate moieties of preconjugation-specific adhesion molecules and thereby might allosterically block interactions with their counterparts. To identify preconjugation-specific alterations in number or localization of Concanavalin A-binding glycoconjugates, we probed western blots of total cell proteins or fixed cells, respectively, with digoxigenin-labeled Concanavalin A. On Concanavalin A blots 20 different Concanavalin A-binding glycoconjugates were identified in mating-competent cells. Localization of Concanavalin A-binding sites on mating-competent cells by light microscopy resulted in predominant labeling of a comma-shaped structure near the paroral membranelle. During the preconjugation period no changes in number or localization of Con A-binding glycoconjugates were detected. Possible reasons are discussed.