Spectroscopic and structural analysis of somatic and N-domain angiotensin I-converting enzyme isoforms from mesangial cells from Wistar and spontaneously hypertensive rats

Angiotensin I-converting enzyme (ACE) plays a key role in the renin-angiotesin aldosterone cascade. We analysed the secondary structure and structural organization of a purified 65kDa N-domain ACE (nACE) from Wistar rat mesangial cells, a 90kDa nACE from spontaneously hypertensive rats and a 130kDa somatic ACE. The C-terminal alignment of the 65kDa nACE with rat ACE revealed that the former was truncated at Ser482, and the sequence of the 90kDa nACE ended at Pro629. Protein's secondary structure consisted predominantly of α-helices. The 90 and 65kDa isoforms were the most stable in guanidine and at low pH, respectively. Enzymatic activity decreased with loss in secondary structure, except in the case of guanidine HCl where the 90kDa fragment loses its secondary structure faster than its enzymatic activity. We identified and characterized the activity and stability of these isoforms and these findings would be helpful on the understanding of the role of nACE isoforms in hypertension. © 2010 Elsevier B.V.