[The biological significance of a basic protein (BBSP) from the seminalplasma of the bull].

1. The mean concentration of BBSP in the seminal bull plasma is 1.53 + 0.30 mg/ml. This con­ centration decreases about 40% after 14 days storage at 4 °C. 2. There is only a small correlation between the concentration of BBSP in the seminalplasma and its fertilization capacity. 3. An artificial doubling of the normal BBSP concentration does not change the results of an artificial insemination. 4. The genital tract of bull has been investigated with immunofluorescent antibodies on the presence of BBSP. The results were negative. 5. Exprimed sperm from tail of epididymis didn’t show fluorescence after treatment with cor­ respondent antibodies. However washed ejaculated sperms had a distinct fluorescence in the middle piece. After incubation of washed sperms with BBSP containing seminal plasma the entire surface of the sperms showed an additional immunofluorescence. 6. From this it is concluded that BBSP develops or is concentrated in the middle piece of sperms during its stay in the head of the epididymis. During the ejaculation a portion of the sperms is destroyed and therefore BBSP enters the seminalplasma. The sperms contain on the whole surface strongly negatively charged groups especially neuraminic acids. The BBSP binds to these groups. So the electrophoretic mobility of ejaculated sperms is reduced. 7. The BBSP has a strong leukotactic activity. This is the probable reason for the phagocytotie activity of seminal plasma.