Developmental profile of a caltrin-like protease inhibitor, P12, in mouse seminal vesicle and characterization of its binding sites on sperm surface

We examined the developmental profile of a kazal-type! trypsin inhibitor (P 12) of M-r 6126 in mouse seminal vesicle, characterized its binding sites o n the surface of sperm, and assessed its effect on Ca2+ uptake by spermatoz oa. Among the genital tracts of adult mice, P12 was found only in the male accessory glands including seminal vesicle, coagulating gland, and prostate . It was immunolocalized on the luminal epithelium of the primary and secon dary folds in both the seminal vesicle and coagulating gland, and on the fo lds projecting into the lumen of the glandular alveolus in the prostate. Th e protein and its RNA message in seminal vesicle did not appear in the prep ubertal period, but expression coincided with maturation. Castration of adu lt mice resulted in cessation of P12 expression. Treatment of the castrated mice with testosterone propionate in corn oil restored the protein express ion in the seminal vesicle. Spermatozoa collected from caudal epididymis we re devoid of P12, Cytochemical study illustrated a P12-binding region on th e anterior acrosomes of cells preincubated with P12, Analysis of equilibriu m data from the binding assay using I-125-P12 with a Scatchard plot showed a single type of P12-binding sites on sperm, with an apparent dissociation constant of 70.15 +/- 5.25 nM and the capacity of 1.49 +/- 0.06 x 10(6) bin ding sites/cell. The protein could serve as a calcium transport inhibitor t o suppress a great extent of Ca2+ uptake by spermatozoa, The immunohistoche mical staining patterns of testis revealed that the P12-binding sites appea red on postmeiotic cells such as spermatids and spermatozoa, but were absen t in Leydig cells, Sertoli cells, spermatogonia, and spermatocytes in semin iferous tubules.