ACE and ACE2 activities both show pH dependency.

The pH dependence of recombinant ACE expressed in CHO cells were studied (Mol Pharmacol, 51:1070–1076, 1997). For ACE activity assay the pH dependence of Hip-Lys-Pro or Hip-Ala-Pro substrate hydrolysis was determined in 100 mM Tris-maleate buffer over a pH range of 5.0–9.2. Assays were also performed using 100 mM HEPES, pH 6.8–8.0, or potassium phosphate, pH 5.5–8.0, buffers. Chloride activation was determined in 100 mM potassium phosphate, pH 8.0, and 0–600 mM NaCl. The pH optima reported for ACE was pH 8.0.

For renal ACE2 activity it was reported that the pH optima is ~7.5 (Biol Sex Diff 2010, 1:6).Renal ACE2 activity was measured using the caspase-1 fluorogenic substrate 7-Mca-Tyr-Val-Ala-Asp-Ala-Pro-Lys(Dnp)-OH (R&D Systems, MN, USA), pH dependency of ACE2 activity is striking when product formation at 150 min is plotted as a function of pH with max activity at pH 7.5. The ACE2 activity was reported to be significantly reduced below pH 6.5 and at pH 8.0.

I am sharing these two papers as a combined file as ready references.

Good luck!!

Thank you very much Amritlal for adding your valuable answers over here. In in vivo, what is the location of these two enzymes-either are they located in cytosol or attached to the plasma membrane. If they are present at the same location in invivo, definitely at same pH both do not show optimum activity. Please can you explain this situation in invivo conditions.

 I have carried out ACE-2 activity at different pH ranging from 1 to 7.4 and i found maximum activity for ACE-2 was at 5.5. 

I used Mca-YVADAPK(Dnp) substrate. 

It is generally not realised, though Danielli in the 1940s, Weiss , Wallach’s book Seaman and I frequently emphasized that the surface pH could be lower by up to 1 to even two units lower. Thus, if the optimum activity is at pH, the operational pH might be 5 or even lower. Clinicians, biotechnologists please note. Clinicians know how critical the pH is for patients and also for mountain Everest climbers. Do not ignore basic research data.