**6. Thimet oligopeptidase**

Thimet oligopeptidase [EC 3.4.24.15, 80 kDa] is primarily a soluble metalloendopeptidase that resides within the cell. Similar to neprilysin, thimet oligopeptidase prefers aromatic and hydrophobic residues and cleaves multiple peptide substrates. In regard to the RAS, thimet oligopeptidase hydrolyzes Ang I exclusivity at the Pro-Phe bond to form Ang-(1-7) (**Figure 1**). We recently showed that both neprilysin and thimet oligopeptidase contributed to the processing of Ang I to Ang-(1-7) within isolated mitochondria [21]. In the human proximal tubule HK-2 cell line, cytosolic thimet oligopeptidase was the sole activity responsible for the generation of Ang-(1-7) from exogenous Ang I [57]. Moreover, thimet oligopeptidase activity in isolated nuclei processed Ang I exclusively to Ang-(1-7) and may be a potential candidate that contributes to the nuclear levels of Ang-(1-7) within the cell [22]. The RAS was originally characterized as a classic endocrine or circulating system, but there is very compelling evidence for the intracellular expression of the RAS peptides, receptors, and synthetic components [7, 54, 58–60]. It is presently unclear the cellular mechanisms for the intracellular expression of Ang II or Ang-(1-7), although the intracellular peptidase thimet oligopeptidase may play a role in the cellular Ang-(1-7) axis.
