Angiotensin converting enzyme (ACE) is a zinc-containing dipeptidase that converts angiotensin I to angiotensin II, a powerful vasoconstrictor and smooth muscle growth factor. ACE activity has been shown to be dynamically regulated by hormones, ACE inhibitors, and endothelial cell growth state. To study how ACE expression is regulated, we isolated and sequenced the bovine ACE gene using both ACE-specific cDNA and genomic clones. Bovine ACE cDNA encodes a single polypeptide of 1,306 residues with a molecular mass of 150 kd. Bovine ACE is approximately 80% homologous to that of other species. It contains two homologous domains of equal size. Alignment of ACE sequences from bovine, human, mouse, and rabbit reveals that during evolution both domains have been highly conserved. We used the bovine ACE cDNA to study regulation of ACE gene expression during density-dependent growth arrest. As endothelial cells became growth-arrested (6 days after confluence), there was a 12-fold increase in ACE activity and a 90% decrease in DNA synthesis. Immunocytochemically detectable ACE markedly increased in growth-arrested cells. The increase in ACE was due to increased ACE gene expression, as assayed by RNase protection, which showed a 20-fold increase in ACE-specific mRNA. The present study shows that bovine ACE is highly regulated by endothelial cell growth state at the level of protein and mRNA expression. Such dynamic regulation may have important consequences for angiotensin II production during endothelial cell proliferation after arterial injury.