EPAC and PKA-Inactivation

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Binding Reaction

EPAC:

$\text{EPAC} \rightleftharpoons \text{inactiveEPAC}$

PKA:

$\text{PKA} \rightleftharpoons \text{inactivePKA}$

Kinetic Equation

EPAC:

$v_{\text{EPAC-Inactivation}} = \frac{v_{max} \cdot [\text{EPAC}] \cdot (1-\frac{[\text{inactiveEPAC}]}{[\text{EPAC}] \cdot K_{eq}})}{Km_{\text{EPAC}} \cdot (1 + \frac{[\text{EPAC}]}{Km_{\text{EPAC}}} + \frac{[\text{inactiveEPAC}]}{Km_{\text{inactiveEPAC}}})}$

PKA:

$v_{\text{PKA-Inactivation}} = \frac{v_{max} \cdot [\text{PKA}] \cdot (1-\frac{[\text{inactivePKA}]}{[\text{PKA}] \cdot K_{eq}})}{Km_{\text{PKA}} \cdot (1 + \frac{[\text{PKA}]}{Km_{\text{PKA}}} + \frac{[\text{inactivePKA}]}{Km_{\text{inactivePKA}}})}$

Final Parameter

EPAC:

$v_{max} = 872.757 \pm 90.727\ \frac{M}{s}$

$K_{m} = 8320.35 \pm 6733.4\ M$

PKA:

$v_{max} = 13519 \pm 1405.4 \frac{M}{s}$

$K_{m} = 9681.2 \pm 11752\ M$

Notes

The equilibrium constant of the binding of cAMP to EPAC is used. As k_cat the value calculated by the model by Xu et al (2010) and the averaged relative standard error is used. As K_m-values the same values as the one of the activation process by an argonist are used and as uncertainty the same relative error is assumed.

Km_P value and equilibrium constant

The K_m value for the product is assumed to be similar to but slightly smaller than the the K_m value of the substrate because of the similarity of the both species. Therefore the K_m value of the substrate is multiplied by 0.95 to gain the one of the product and the uncertainty is increased by increasing the error on Km_substrate by 50%.

For information about the equilibrium constant please see here.