Chicken lacks the testis specific isozyme of angiotensin converting enzyme found in mammals.

Chicken angiotensin converting enzyme (ACE) cDNA was cloned based on homology to the mouse ACE sequence. The chicken ACE protein is highly homologous to the somatic isozyme of ACE found in human, mouse, bovine, and rabbit. Like the mammalian somatic forms, the chicken enzyme consists of two putative zinc binding sites at the center of two homologous domains. All known functional residues are absolutely conserved. Unlike the mammals, no evidence for a single domain, testis specific form of ACE was found in the chicken testis by either Northern blot or enzyme assay. This result is unexpected since the adult mammalian testis expresses one of the highest tissue levels of ACE.