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Biology of Reproduction, Vol 21, 857-866, Copyright © 1979 by Society for the Study of Reproduction
1 Department of Gynecology and Obstetrics
and The C. S. Mott Center for Human Growth and Development,
Wayne State University School of Medicine,
Detroit, Michigan 48201 This study was made to determine the degree of immunologic similarity or dissimilarity between rabbit proacrosin and acrosin and thereby to elucidate the extent of molecular change that
occurs when proacrosin is converted to acrosin. A highly sensitive and specific radioimmunoassay
for rabbit acrosin was developed and used to quantify the immunologic reactions. Testicular proacrosin was purified, but not to homogeneity, by sequential acid extraction, gel filtration, cation
exchange and Concanavalin A chromatography. Acrosin immunogen was purified to homogeneity
by subjecting activated proacrosin to affinity chromatography on CH-Sepharose benzamidine. A
monospecific antiserum against acrosin was obtained from female rabbits following immunization
with 500 µg doses of TLCK (tosyl-lysine-chloromethyl-ketone) treated acrosin 6 weeks apart. A
labeled antigen (specific activity 40 µCi/µg) for the radioimmunoassays was obtained by iodination
of TLCK treated acrosin by the chloramine T method. All subsequent immunologic tests were
performed in the presence of 0.05 M benzamidine. Qualitative indications of immunologic dissimilarity between proacrosin and acrosin were obtained in Ouchterlony tests where proacrosin
gave no precipitin band while acrosin gave a strong band against the antiacrosin serum. For the
radioimmunoassays, serial dilutions of proacrosin, representing progressive stages in the activation,
were used to generate dose response curves with the antiacrosin serum. Calculations based on the
50% displacement values obtained from these curves showed that the cross reaction between
unactivated proacrosin and antiacrosin antibody was only 1.8% of that obtained with fully activated proacrosin (acrosin) and the same antibody. The results indicate that a major conformational
change occurs when proacrosin is activated to acrosin.
Note:
ACKNOWLEDGMENTS
Supported by the World Health Organization Grant
75060 and NICHD contract N01-HD-3-2773.
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