Selective substrate for angiotensin-converting enzyme 2 (ACE2), an ACE homolog which differs in its specificity and physiological role from ACE. The internally quenched fluorescent (FRET) substrate is potentially useful in applications such as high-throughput screening of ACE2 inhibitors (Km = 23 µM, kcat/Km = 3.5 · 10⁴ M⁻¹s⁻¹).