To determine whether Ang-(1-9) is active per se or it becomes active only after conversion to Ang-(1-7), Chen et al. [55] examined the metabolism of Ang I, Ang-(1-9) and Ang-(1-7) in stably transfected CHO cells that express human ACE and human bradykinin B2 receptors coupled to green fluorescent protein (B2GFP). They found that Ang-(1-9) was hydrolyzed 18 times slower than Ang I and 30% slower than Ang-(1-7). Ang-(1-9) inhibited ACE and it resensitized the desensitized B2GFP receptors, independently of ACE inhibition [55] . This is reflected by release of arachidonic acid through a mechanism involving cross-talk between ACE and B2 receptors. They concluded that Ang-(1-9) enhanced bradykinin activity, probably by acting as an endogenous allosteric modifier of the ACE and B2 receptor complex. Therefore, when ACE inhibitors block conversion of Ang I, other enzymes like ACE2 can still release Ang I metabolites like Ang-(1-9) and enhance the efficacy of ACEIs.