Binding of 125I-succinylated concanavalin A to bovine spermatozoa

This study characterizes interactions of 125I-succinylated concanavalin A (125I-sucConA) with plasma membranes of intact bovine spermatozoa. Maximum binding was achieved by 30 min at 24 degrees C. Reversibility of binding was established by displacement of bound ligand with nonradioactive sucConA. Seventy-five percent of the bound sucConA was removed as a single kinetics class. When alpha-methylmannoside was used as a competitive ligand, 90% of the sucConA was removed. Saturability of binding sites, however, was not achieved over the concentration range of 125I-sucConA examined (0.13 micrograms/ml to 77 micrograms/ml). Binding kinetics of this system was complex and linear Scatchard analysis was not appropriate. The degree of 125I-sucConA binding to spermatozoa was influenced (P less than 0.01) by different iodination batches of 125I-sucConA. Complications due to iodination of ligand and the complex nature of its interaction with the membrane preclude the use of 125I-sucConA for a quantitative study of sperm membrane features.