Regular paperKinetic calibration of the calcium indicator arsenazo III. I. Stopped-flow spectroscopy

Add time:09/08/2019    Source:sciencedirect.com

Stopped-flow studies of the calcium-arsenazo III (Ar) system exhibit reaction time constants ranging from 4 to 20 ms, mainly caused by the formation of CaAr and CaAr2 complexes ([Ca]0 = 10 μM to 10 mM, [Ar]0 = 10 μM to 50 μM). At total concentrations [Ca]0 ≥ 100 μM an additional slow reaction mode with time constants of 100 to 600 ms has been found, which is attributed to the formation of the Ca2Ar complex according to Ca + CaAr ⇌ harp over l Ca2Ar. The rate coefficients of association and dissociation are, respectively, k+ = 900 M−1 · s−1 and k− = 1.8 s−1, yielding K = k+/k− = 500 M−1. In biophysics and cell biology arsenazo III may be used to monitor the kinetics of micromolar Ca-concentration changes in the time range ≥ 50 ms. If the optical signal is properly deconvoluted, the time range may be extended to 5 ms. An improved method for purifying arsenazo III is communicated.

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