Table 2. Parameters used for simulation of GPCR-activation of GIRK.
k12: The rate of formation of the productive GPCR-G protein complex (Sungkaworn et al., 2017). k21: The rate of dissociation of the productive GPCR-G protein complex (Sungkaworn et al., 2017). k23: The rate of nucleotide exchange and subsequent dissociation of GPCRs, Gα(GTP), and Gβγ (Sungkaworn et al., 2017). k32: The rate of the reverse reaction of nucleotide exchange and dissociation of GPCRs and G proteins. k34: The rate of GTP hydrolysis, based on Breitwieser and Szabo, 1988. k43: The rate of the reverse reaction of GTP hydrolysis. k45: The on-rate between Gα(GDP) and Gβγ, adapted from Sarvazyan et al., 1998. k54: The off-rate between Gα(GDP) and Gβγ, calculated based on k45 and Kd = 3 nM (Sarvazyan et al., 1998). k56: The on-rate between the GIRK and Gβγ is diffusion limited (Wang et al., 2016). k65: The off-rate between the GIRK and Gβγ were calculated based on k56 and our previous Kd measurement (Shea et al., 1997).
| Reaction | Forward-rate | Backward-rate | Note |
|---|---|---|---|
| R* + Gα(GDP)βγ ⇌ R*-Gα(GDP)βγ | 1 µM−1 sec−1 (k12) | 1 sec−1 (k21) | Sungkaworn et al., 2017 |
| R*-Gα(GDP)βγ ⇌ R* + Gα(GTP) + Gβγ | 1 sec−1 (k23) | 0 M−2 sec−1 (k32) | Sungkaworn et al., 2017 |
| Gα(GTP) ⇌ Gα(GDP) + Pi | 2 sec−1 (k34) | 0 M−1 sec−1 (k43) | Breitwieser and Szabo, 1988 |
| Gα(GDP) + Gβγ ⇌ Gα(GDP)βγ | 0.7 × 106 M−1 sec−1 (k45) | 0.002 sec−1 (k54) | Sarvazyan et al., 1998 |
| GIRK-βγn-1 + (5 - n)Gβγ ⇌ GIRK-βγn + (4 - n)Gβγ | (5 - n) × 1 × 107 M−1 sec−1
((5 - n) × k56) |
n × µn-1 × 600 sec−1
(n × µn-1 × k65) |
Shea et al., 1997; Wang et al., 2016 |