PROTEIN-SYNTHESIS AND SECRETION BY THE EPIDIDYMIS OF THE BRUSHTAIL POSSUM, TRICHOSURUS-VULPECULA

In this study of brushtail possums, proteins present in epididymal flu id and not present in blood plasma and those that become associated wi th spermatozoa as they pass along the tract were investigated. At leas t 19 proteins were present in epididymal fluid in the various regions of the tract that were not detected in serum. Some of these may be pre sent on the sperm plasmalemma. Six proteins were extracted from caput spermatozoa (M-r 117 000, 103 000, 87 500, 85 000, 62 000 and 33 000) that did not appear in the caudal sperm extracts. Eight proteins (M-r 50 000, 49 000, 32 000, 27 000, 26 500, 25 000, 24 500 and 18 000) wer e localized to caudal sperm extracts. These findings suggest that some sperm proteins are lost or modified, whereas others are added to the sperm plasma membrane during epididymal transit. In vitro incorporatio n of [S-35]methionine by the epididymal tissue showed that the distal caput and corpus are the most active regions in the synthesis and secr etion of proteins. Four caudal epididymal proteins (M-r 72 000, 31 000 , 26 500 and 21 000) were partially sequenced. Those of M-r 31 000 and 26 500 had the same N-terminal amino acid sequence suggesting post-tr anslational modification of the same protein; they showed homology to a retinoic acid-binding protein. The protein of M-r 72 000 was found t o be homologous to a-fetoprotein, whereas the protein of M-r 21 000 sh owed no significant homology to any protein in the database. These res ults show that the lumen of the epididymis has many proteins that are not present in the blood, some of which appear to become associated wi th spermatozoa during epididymal transit.