Lysogenic Activity of Enhancer Caltrin and the Influence of Phospholipids on its Expression1

Enhancer caltrin permeabilizes the plasma membrane of bovine epididymal spermatozoa as indicated by the release of hyaluronidase from the acrosome and lactate dehydrogenase (LDH) from the sperm cytosol. A previously reported increased calcium uptake by the sperm in the presence of enhancer caltrin was apparently due, in part, to calcium entry into the mitochondria, which had become accessible to external calcium. At 37 microM (200 micrograms/ml), enhancer caltrin released about 30% of the total hyaluronidase in the acrosome and 50% of the cytosolic LDH from epididymal sperm (4 x 10(7)/ml). This event was prevented by phosphatidylserine (PS), presumably through caltrin-phospholipid complex formation, whereas phosphatidylcholine (PC) was ineffective. Cardiolipin induced the release of LDH and this too was prevented by enhancer caltrin. Lysophosphatidylserine (LPS), on the other hand, potentiated the lysogenic activity of enhancer caltrin, promoting the release of the full complement of hyaluronidase and LDH even at a molar ratio of only 1:1 with caltrin. The effect of mixtures of LPS and PS on the lysogenic property of enhancer caltrin was investigated, and it was found that PS suppressed the potentiating effect of LPS. Release of hyaluronidase and LDH took place only when the LPS/PS molar ratio was greater than 2. The implications of these findings for the role of caltrin in mammalian fertilization are discussed.