Figure 2. Stability of the zymogen proFheCL1Gly²⁵ and mature FheCL1 at various pH values.

(A) Far-UV CD spectra of 5.3 µM FheproCL1Gly²⁵ in 50 mM sodium acetate buffer, pH 4.0 and in 50 mM sodium phosphate buffer, pH 7.5. (B) Enzymatic stability of 6.0 µM mature FheCL1 at 37°C and in 0.1 M buffers over the pH range 2.5–9.0. Enzyme activity was monitored at various time-points by diluting aliquots of the reactions into 0.1 M sodium acetate buffer, pH 5.5, containing 3 mM DTT before addition of 5 µM Z-Phe-Arg-NMec.