Carbohydrate recognition systems in amphibians: primitive alpha 2-macroglobulin receptors

Two alpha-macroglobulins were isolated from the plasma of the frog. Murine clearance studies were performed with these proteins after they were reacted with proteinase. These studies indicated that clearance behavior was more complex than observed with avian or human homologues, since it involved not only specific receptors for the complex, but also carbohydrate recognition. Recognition of one of these macroglobulins by both the alpha-macroglobulin receptor and carbohydrate receptors required conformational change in the inhibitor. Clearance studies were then performed in frogs to probe the nature of carbohydrate receptor recognition. Model glycoproteins were employed to avoid the problem of heterogeneous carbohydrate end groups in the alpha-macroglobulins. These studies demonstrated that the N-acetylglucosamine/mannose receptor is the major carbohydrate recognition system in frogs.