| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | RecLigandBinding | Gq
Pathway No. 125 | 16.8
(uM^-1 s^-1) | 10
(s^-1) | Kd(bf) = 0.5952(uM) | - | Substrate:
mGluR
Glu
Products:
Rec-Glu
|
| From Martin et al FEBS Lett 316:2 191-196 1993 we have Kd = 600 nM Assuming kb = 10/sec, we get kf = 10/(0.6 uM * 6e5) = 2.8e-5 1/sec/# The off time for Glu seems pretty slow: Nicoletti et al 1986 PNAS 83:1931-1935 and Schoepp and Johnson 1989 J Neurochem 53 1865-1870 indicate it is at least 30 sec. Here we are a little faster because this is only a small part of the off rate, the rest coming from the Rec-Gq complex. | | 2 | Rec-bind-Gq | Gq
Pathway No. 125 | 0.6
(uM^-1 s^-1) | 1
(s^-1) | Kd(bf) = 1.6667(uM) | - | Substrate:
G-GDP
mGluR
Products:
Rec-Gq
|
| From Berstein et al 1992 JBC 267(12):8081-8088 we know that 15-40% of Gq binds, GTP_gamma_S. Also about 20-30% of Gq is bound to GTP. To get to these values the receptor-Gq amount should be similar. These rates are designed to give that steady state with a fast tau of 1 sec. | | 3 | Glu-bind-Rec-Gq | Gq
Pathway No. 125 | 16.8
(uM^-1 s^-1) | 0.1
(s^-1) | Kd(bf) = 0.006(uM) | - | Substrate:
Glu
Rec-Gq
Products:
Rec-Glu-Gq
|
| From Fay et al kb3 = kb = 1.06e-3 which is rather slow. k+1 = kf = 2.8e7 /M/sec= 4.67e-5/sec use 5e-5. However, the Kd from Martin et al may be more appropriate, as this is Glu not the system from Fay. kf = 2.8e-5, kb = 10 Let us compromise. since we have the Fay model, keep kf = k+1 = 2.8e-5. But kb (k-3) is .01 * k-1 from Fay. Scaling by .01, kb = .01 * 10 = 0.1 | | 4 | Antag-bind-Rec-G
q | Gq
Pathway No. 125 | 60
(uM^-1 s^-1) | 0.01
(s^-1) | Kd(bf) = 0.0002(uM) | - | Substrate:
Rec-Gq
mGluRAntag
Products:
Blocked-rec-Gq
|
| The rate consts give a total binding affinity of under 0.2 nM, good for a strong antagonist. | | 5 | Rec-Glu-bind-Gq | Gq
Pathway No. 125 | 0.006
(uM^-1 s^-1) | 0.0001
(s^-1) | Kd(bf) = 0.0167(uM) | - | Substrate:
G-GDP
Rec-Glu
Products:
Rec-Glu-Gq
|
| This is the k1-k2 equivalent for enzyme complex formation in the binding of Rec-Glu to Gq. See Fay et al Biochem 30 5066-5075 1991. Closer reading of Fay et al suggests that kb <= 0.0001, so kf = 1e-8 by detailed balance. This reaction appears to be neglible. | | 6 | Basal-Act-G | Gq
Pathway No. 125 | 0.0001
(s^-1) | 0
(uM^-1 s^-1) | - | - | Substrate:
G-GDP
Products:
G*GTP
BetaGamma
|
| This is the basal exchange of GTP for GDP. So slow as to be nearly negligible. | | 7 | Trimerize-G | Gq
Pathway No. 125 | 6
(uM^-1 s^-1) | 0
(s^-1) | - | - | Substrate:
G*GDP
BetaGamma
Products:
G-GDP
|
| kf == kg3 = 1e-5 /cell/sec. As usual, there is no back-reaction kb = 0 | | 8 | Inact-G | Gq
Pathway No. 125 | 0.0133
(s^-1) | 0
(s^-1) | - | - | Substrate:
G*GTP
Products:
G*GDP
|
| From Berstein et al JBC 267:12 8081-8088 1992, kcat for GTPase activity of Gq is only 0.8/min. | | 9 | Activate-Gq | Gq
Pathway No. 125 | 0.01
(s^-1) | 0
(uM^-2 s^-1) | - | - | Substrate:
Rec-Glu-Gq
Products:
G*GTP
BetaGamma
Rec-Glu
|
| This reaction is the critical one for activation of Gq. It probably encapsulates multiple steps. In this approximation the receptor-ligand- Gprotein complex splits up into GTP.Galpha, rec.ligand complex, and Gbetagamma. There is a hidden step of exchange of GDP for GTP. The reaction does not take these into account since it is assumed that both GTP and GDP levels are tightly regulated by metabolic control. This is the kcat==k3 stage of the Rec-Glu ezymatic activation of Gq. From Berstein et al actiation is at .35 - 0.7/min From Fay et al Biochem 30 5066-5075 1991 kf = .01/sec From Nakamura et al J physiol Lond 474:1 35-41 1994 see time courses. Also (Berstein) 15-40% of gprot is in GTP-bound form on stim. |
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