Cloning, sequencing, and characterization of LDH-C4 from a fox testis cDNA library.

A full-length cDNA encoding the sperm-specific enzyme lactate dehydrogenase-C4 was isolated from a fox testis cDNA expression library and sequenced. The deduced translated protein sequence was shown to be 86% identical to that of human LDH-C4. In the fox testis, mRNA encoding LDH-C4 was first detected in pachytene spermatocytes. The LDH-C4 protein monomer was identified in Western blots of sperm membrane extracts as having a molecular weight of approximately 35,000, consistent with the monomeric size of this subunit previously identified in sperm from other species. The LDH-C4 protein is localized on the sperm plasma membrane overlying the principal piece of the tail. Based on the available sequence data, we were able to identify an epitope within the N-terminal region of the LDH-C4 amino-acid sequence which when administered to female foxes is antigenic and produces antibodies capable of recognizing the native protein.