Construction of a Turn Off-On-Off Fluorescent System Based on Competitive Coordination of Cu²⁺ between 6,7-Dihydroxycoumarin and Pyrophosphate Ion for Sensitive Assay of Pyrophosphatase Activity

Figure 4

Fluorescence responses of DHC (500 μM) (curve A) and Cu²⁺-DHC (Cu²⁺: 200 μM, DHC: 500 μM) complex with PPi (curves B to G: 0, 10, 30, 50, 100, and 200 μM) in HEPES aqueous buffer (10 mM, pH 6.5). Inset shows fluorescence changes of Cu²⁺-DHC (Cu²⁺: 200 μM, DHC: 500 μM) complex at 475 nm as a function of PPi concentration. Other reaction conditions are the same as Figure 1.