AMINOPEPTIDASE-B FROM THE RAT TESTIS IS A BIFUNCTIONAL ENZYME STRUCTURALLY RELATED TO LEUKOTRIENE-A(4) HYDROLASE

An aminopeptidase B (Ap-B) was previously purified to homogeneity from rat testis extracts and characterized, In the present work, by using oligonucleotides selected on the basis of partial amino acid microsequ ences of pure Ap-B and PCR techniques, the nucleotide sequence of a 2. 2-kb cDNA was obtained, The deduced amino acid sequence corresponds to a 648-residue protein (72.3 kDa) containing the canonical ''HEXXHX(18 )E'' signature, which allowed its classification as a member of the MI family of metallopeptidases, It exhibits 33% identity and 48% similar ity with leukotriene-A(4) hydrolase, a relation further supported by t he capacity of Ap-B to hydrolyze leukotriene A(4). Both enzymes also w ere closely related to a partially sequenced protein from Dictyosteliu m discoideum, which might constitute the putative common ancestor of e ither aminopeptidase or epo tide hydrolase, or both, Ap-B and its mRNA were detected in the germ line and in the Sertoli and peritubular cel ls of the seminiferous tubules, Because the enzyme was found in the me dium conditioned by spermatocytes and spermatids and in the acrosome d uring spermatozoa formation, together these observations suggested an involvement of this exometallopeptidase in the secretory pathway, It i s concluded that this ubiquitous enzyme may be Involved in multiple pr ocessing mechanisms.