Heparin Binding Sites in the Human Spermatozoa Membrane

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Abstract
The existence in the human spermatozoa membrane of a receptor-like functional group for heparin was studied. Incubation of whole spermatozoa with [3H]heparin induced the specific binding of 745 .+-. 112 pmol of heparin per 5 .times. 107 sperm cells with an intrinsic Kd = 3.6 .times. 10-6 M. The specificity of binding was shown by the lack of competence in the binding process of some other glycosaminoglycans used at concentrations 20 times higher than heparin. However, dextran sulfate was a very efficient competitive agent. Autoradiography experiments showed that labeling was almost completely restricted to sperm cells in the process of nuclear decondensation. This technique showed the presence of a high amount of radioactive heparin in the isolated sperm membranes even after several washings. Heparin may participate both in the final part of the capacitation process (acrosome reaction) and in the decondensation of sperm nuclei.