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Biology of Reproduction, Vol 13, 83-93, Copyright © 1975 by Society for the Study of Reproduction

Proacrosin from Rabbit Epididymal Spermatozoa: Partial Purification and Initial Biochemical Characterization

STANLEY MEIZEL 1, and SUDHIR K. MUKERJI 1

1 Department of Human Anatomy, School of Medicine, University of California, Davis, California 95616, U.S.A.


Proacrosin, the zymogen form of acrosin was extracted with 0.25N H2SO4 from unwashed rabbit cauda epididymal spermatozoa. Sephadex G-75 column chromatography of the extract resolved two peaks of epididymal sperm proacrosin, both of which contained low amounts of acrosin prior to activation (a total of 5 percent of the final acrosin activity obtained from complete activation of proacrosin), and were free of trypsin inhibitor. The peak eluted first (peak I) represented 85 percent of the total proacrosin and had an apparent molecular weight (MW) of 73,000 as determined by Sephadex G-100 column chromatography. Complete "autoactivation" of sperm proacrosin peak I resulted in the production of an acrosin with a MW of 38,000. Proacrosin was also found in washed epididymal sperm uncontaminated by free cytoplasmic droplets or epididymal fluid.

Sperm proacrosin "autoactivation" appeared to be a second order autocatalytic process in which the product of the activation accelerated its own formation. The "autoactivation" was stimulated by Ca++ and inhibited by Zn++.

These properties of sperm proacrosin agree with our previous data from studies of rabbit testis proacrosin. Also the acrosin obtained by "autoactivating" the sperm and testis proacrosins, had similar apparent Km values for BANA (7.8-10.5 x 10-5M), BAEE (2.1-4.3 x 10-5M) and TAME (2.4-3.3 x 10-5M), similar pH optima (pH 8.2-8.4), and were similarly inhibited by several trypsin inhibitors. These results suggest strongly that rabbit epididymal sperm and rabbit testis proacrosin are identical proteins.

Conversion of sperm proacrosin to acrosin (involving the hydrolysis of at least one peptide bond) would appear to be necessary if acrosin plays a role in fertilization.

 Submitted on February 3, 1975
Accepted on March 31, 1975




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T. Wincek, R. Parrish, and K. Polakoski
Fertilization: a uterine glycosaminoglycan stimulates the conversion of sperm proacrosin to acrosin
Science, February 9, 1979; 203(4380): 553 - 554.
[Abstract] [PDF]


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Copyright © 1975 by the Society for the Study of Reproduction.