Measuring the steady-state properties of Ca²⁺ indicators with a set of calibrated [Ca²⁺] solutions

Measuring the Ca²⁺-binding kinetics of proteins

Ca(2+)-binding proteins (CBPs) are instrumental in the control of Ca(2+) signaling. For the transduction of a change in intracellular Ca(2+) concentration into a cellular biochemical or biophysical action, it is necessary for Ca(2+) to bind specific Ca(2+)-binding proteins (CBPs) that relay the Ca(2+) signal. The competition for Ca(2+) between the various CBPs plays an essential and direct role in this transduction and in the resulting biochemical message. Therefore, a thorough understanding of Ca(2+) signaling necessitates appreciating the kinetic properties of all the relevant CBPs. Unfortunately, most conventional techniques used to measure Ca(2+)-binding kinetics are too slow to determine accurately the fast binding kinetics of most CBPs. To address this problem, we have developed an ultrafast in vitro technique for measuring the Ca(2+)-binding properties of CBPs following flash photolysis of caged Ca(2+). We introduce here the protocols that are necessary for the data collection associated with this technique.

Measuring the rate constants of Ca²⁺ indicators

Fluorescent Ca(2+) indicators are widely used to measure the concentration of free Ca(2+) ([Ca(2+)](free)) in biological processes. To determine the exact kinetics of changes in [Ca(2+)](free) and the processes underlying these changes (e.g., Ca(2+) binding to Ca(2+)-binding proteins), it is necessary to know the exact binding properties of the indicator used. Here, we describe how to determine the binding rate constants (k(on) and k(off)) of Ca(2+) indicators.

Collecting data to determine the Ca²⁺-binding properties of DM-nitrophen and proteins

Conventional techniques used to measure Ca(2+) binding are too slow to determine accurately the fast binding kinetics of most molecules such as Ca(2+)-binding proteins (CBPs). We have developed an ultra-fast in vitro technique for measuring the Ca(2+)-binding properties of CBPs following flash photolysis of caged Ca(2+). Although the details of the setup, the mathematics, and the analysis involved in this technique have been published elsewhere, many of the practical details regarding the actual measurements have, until now, only been described minimally. Here, we present a protocol to gather the data necessary to determine the kinetic properties of a caged-Ca(2+) compound and a CBP.