NRD CONVERTASE - A PUTATIVE PROCESSING ENDOPROTEASE ASSOCIATED WITH THE AXONEME AND THE MANCHETTE IN LATE SPERMATIDS

N-arginine dibasic convertase is a novel metalloendopeptidase which se lectively cleaves at the N terminus of arginine residues in paired bas ic amino acids, Although present in brain and several other tissues, N RD convertase is particularly abundant in testis, where its expression appeared to be restricted to germ cells. Low levels of both mRNA and its corresponding protein were detected early in spermatogenesis, Howe ver, a marked accumulation of the protein was observed during late ste ps (14 to 19) of spermiogenesis, By electron microscopy, the NRD conve rtase immunoreactivity was localized in the cytoplasm of elongating an d elongated spermatids, with a noticeable concentration at the level o f two microtubular structures, i.e. the manchette and the axoneme. The se observations strongly support the hypothesis that NRD convertase is involved in processing events potentially associated with the morphol ogical transformations occurring during spermiogenesis.