Molecular cloning of human testicular angiotensin-converting enzyme: the testis isozyme is identical to the C-terminal half of endothelial angiotensin-converting enzyme.

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Abstract
Angiotensin-converting enzyme (ACE; EC 3.4.15.1) is a zinc-containing dipeptidyl carboxypeptidase widely distributed in mamalian tissues and is thought to play a critical role in blood pressure regulation. Testis contains a unique, androgen-dependent ACE isozyme of unknown function. We have determined the cDNA sequence for human testicular ACE; it encodes a protein that is identical, from residue 37 to its C terminus, to the second half or C-terminal domain of the endothelial ACE sequence [Soubrier, F., Alhenc-Gelas, F., Hubert, C., Allegrini, J., John, M., Tregear, G. and Corvol, P. (1988) Proc. Natl. Acad. Sci. USA 85, 9386-9390]. The full-length human testis ACE cDNA was constructed from a composite of cloned cDNAs, obtained by a combination of (i) immunoscreening and hybridization screening of a human testicular cDNA library in .lambda.t11 and (ii) hybridization screening of human testis cDNAs constructed with ACE-specific primers and amplified by the polymerase chain reaction. The protein sequence inferred consists of a 732-residue preprotein including a 31-residue signal peptide. The mature polypeptide has a molecular weight of 80,073. The testis enzyme contains the second of the two putative metal-binding sites (His-Glu-Met-Gly-His) identified in endothelial ACE. This indicates that the functionally active catalytic site is within the C-terminal domain of the endothelial enzyme, accounting for the previous finding that these two structurally isozymes are virtually identical catalytically. Of 22 testis ACE cDNAs cloned and sequenced, 3 have unique 5'' regions, consisting of inserted, deleted, or substituted sequences up to 328 base pairs long, which have apparently arisen by alternative pre-mRNA splicing.