

CLOCS Aequorin Calcium Calculator
Calcium concentrations are calculated by two different algorithms.
Algorithm #1
n (number of measurements)
L_{i} (light intensity), counts measured at time point i.
L_{tot} (total counts), [L_{1} + L_{2}... + L_{n}]
L_{max} (remaining counts), L_{tot}  [L_{1} + L_{2}... + L_{i}]
K_{R} (Ca^{2+} association constant)
K_{TR} (equilibrium between binding states), [T]/[R]
nb (number of binding sites)
ratio = (L_{i}/L_{max})^{(1/nb)}
ratio + (ratio·K_{TR})  1
Ca^{2+}[i] = ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
K_{R}  (ratio·K_{TR})
for normal aequorin:
K_{R} (22°C) = 7.23; K_{R} (37°C)= 7.23 · √
2; nb = 2.99; K_{TR} = 120
for mutated aequorin:
K_{R} (22°C) = 5.57; K_{R} (37°C) = 5.57 · √
2; nb = 1.72; K_{TR} = 4046
Brini et al. (1995) J. Biol. Chem 270, 98969903.
Allen et al. (1977) Science 195, 996998.
Algorithm #2
Ca^{2+}[i] = X · [10^{(log(Li/Lmax)  Y)}]^{(1/Z)}
where Z = 2.0;
X = 1; Y = 9 for normal aequorin
X = 1.44; Y = 3.4 for the mutated aequorin.
Rutter et al. (1993) J. Biol. Chem 268, 2238522390.
Mitchel et al. (2001) J. Cell Biol. 155, 4151.
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