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

. 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.