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Histone-mediated agglutination of epididymal spermatozoa and the occurrence of histone receptors on the rat sperm surface

Summary. Exogenous calf thymus whole histones showed a high degree of specificity to cause agglutination of rat epididymal spermatozoa. Histones had markedly greater (~ 5-fold) agglutination activity than did salmon protamine whereas a variety of proteins, including strongly basic ones such as herring protamine sulphate, ribonuclease, cytochrome C and lysozyme, had no detectable agglutination activity. Histones F-3 and F-2a had the greatest activity for cell agglutination. Polyamines (5 mM), sialic acid (5 mM) and basic or acidic amino acids (10 mM) had no effect on histone (~8 µM)-mediated sperm agglutination. ³²P-Labelled histones showed high specificity for binding to intact spermatozoa. The binding was saturable at a histone concentration of ~0·3 mg/ml and nearly completely displaced at saturating concentrations of native histones. Only unlabelled protamines competed to a small extent for binding of ³²P-labelled histones to spermatozoa. The data are consistent with the view that histones bind specifically to sperm surface receptor sites before agglutination of cells.