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Reaction List for pathway Gq (Pathway Number 334) |
| Kd is calculated only for second order reactions, like nA+nB <->nC or nA<->nC+nD, where n is number and A,B,C,D are molecules, where as for first order reactions Keq is calculated. Kd for higher order reactions is not considered. |
| Name | Kf | Kb | Kd | tau | Substrate | Product | |
| 1 | Activate-Gq | 0.01 (s^-1) | 0 (uM^-2 s^-1) | - | - | Rec-Glu-Gq | G*GTP BetaGamma Rec-Glu |
| 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. | |||||||
| 2 | Antag-bind-Rec-G q | 60.0003 (uM^-1 s^-1) | 0.01 (s^-1) | Kd(bf) = 0.0002(uM) | - | Rec-Gq mGluRAntag | Blocked-rec-Gq |
| The rate consts give a total binding affinity of only | |||||||
| 3 | Basal-Act-G | 0.0001 (s^-1) | 0 (uM^-1 s^-1) | - | - | G-GDP | G*GTP BetaGamma |
| kf = kg1 = 0.01/sec, kb = 0. This is the basal exchange of GTP for GDP. | |||||||
| 4 | Glu-bind-Rec-Gq | 16.8003 (uM^-1 s^-1) | 0.1 (s^-1) | Kd(bf) = 0.006(uM) | - | Glu Rec-Gq | 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 | |||||||
| 5 | Inact-G | 0.0133 (s^-1) | 0 (s^-1) | - | - | G*GTP | G*GDP |
| From Berstein et al JBC 267:12 8081-8088 1992, kcat for GTPase activity of Gq is only 0.8/min | |||||||
| 6 | Rec-bind-Gq | 0.6 (uM^-1 s^-1) | 1 (s^-1) | Kd(bf) = 1.6667(uM) | - | G-GDP mGluR | Rec-Gq |
| Lets try out the same kinetics as the Rec-Glu-bind-Gq This is much too forward. We know that the steady-state amount of Rec-Gq should be 40% of the total amount of receptor. This is for a different receptor, still we can try to match the value. kf = 1e-6 and kb = 1 give 0.333:0.8 which is pretty close. | |||||||
| 7 | Rec-Glu-bind-Gq | 0.006 (uM^-1 s^-1) | 0.0001 (s^-1) | Kd(bf) = 0.0167(uM) | - | G-GDP Rec-Glu | 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. kf = 5e-5 which is nearly the same as calculated by Fay et al. (4.67e-5) kb = .04 June 1996: Closer reading of Fay et al suggests that kb <= 0.0001, so kf = 1e-8 by detailed balance. This reaction appears to be neglible. | |||||||
| 8 | RecLigandBinding | 16.8003 (uM^-1 s^-1) | 10 (s^-1) | Kd(bf) = 0.5952(uM) | - | mGluR Glu | Rec-Glu |
| kf = kf from text = 1e7 / M / sec = 10 /uM/sec = 10 / 6e5 / # / sec = 1.67e-5 kb = kr from text = 60 / sec Note that we continue to use uM here since [phenylephrine] is also in uM. 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/# | |||||||
| 9 | Trimerize-G | 6 (uM^-1 s^-1) | 0 (s^-1) | - | - | G*GDP BetaGamma | G-GDP |
| kf == kg3 = 1e-5 /cell/sec. As usual, there is no back-reaction kb = 0 | |||||||
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