| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | remove_glu | Shared_Object_
Synaptic_
Network
Pathway No. 70 | 500
(s^-1) | 1000
(s^-1) | Keq = 2(uM) | 0.001sec | Substrate:
Glu
Products:
synapse
|
| This reaction doubles for arrival as well as removal of glu from the synapse. Assume tau for removal of glu is ~1 msec. We know that diffusion time for arrival of glu from presynaptic side is < 50 usec. Most of the actual synaptic delay has to do with binding to the receptors. | | 2 | Ca-bind-to-Trans
p | CaRegulation
Pathway No. 86 | 3600
(uM^-2 s^-1) | 144
(s^-1) | Kd(bf) = 0.04(uM) | - | Substrate:
Ca_intracell
Ca_intracell
CaTransp
Products:
CaTransp-2Ca
|
| Rates from Lauffenberger and Linderman 1993 Receptors pg 200. Kd = KCa2 = 0.2 uM. | | 3 | cAMP-bind-site-A
1 | PKA
Pathway No. 84 | 75
(uM^-1 s^-1) | 110
(s^-1) | Kd(bf) = 1.4667(uM) | - | Substrate:
R2C2-cAMP2
cAMP
Products:
R2C2-cAMP3
|
| This site has a higher Kd for cAMP. See Ogreid and Doskeland 1982 FEBS Lett 150:1 161-166 | | 4 | CaM-TR2-bind-Ca | CaM
Pathway No. 81 | 72
(uM^-2 s^-1) | 72
(s^-1) | Kd(af) = 1(uM) | - | Substrate:
CaM
Ca
Ca
Products:
CaM-TR2-Ca2
|
| We use the Martin et al 1985 Eur J Biochem 151(3):543-550 rates here, plus the Drabikowski and Brzeska 1982 JBC 257(19):11584-11590 binding consts. All are scaled by 3X to cell temperature. kf = 2e-10 kb = 72 Stemmer & Klee 1994 Biochem 33:6859-6866 have values of : K1=.9, K2=1.1. Assume 1.0uM for both | | 5 | PKC-basal-act | PKC
Pathway No. 71 | 1
(s^-1) | 50
(s^-1) | Keq = 50(uM) | 0.02sec | Substrate:
PKC-cytosolic
Products:
PKC-basal*
|
| Basal activity of PKC is quite high, about 10% of max. See Schaechter and Benowitz 1993 J Neurosci 13(10):4361 and Shinomura et al 1991 PNAS 88:5149-5153. This is partly due to basal levels of DAG, AA and Ca, but even when these are taken into account (see the derivations as per the PKC general notes) there is a small basal activity still to be accounted for. This reaction handles it by giving a 2% activity at baseline. | | 6 | cAMP-bind-site-B
1 | PKA
Pathway No. 84 | 54
(uM^-1 s^-1) | 33
(s^-1) | Kd(bf) = 0.6111(uM) | - | Substrate:
R2C2
cAMP
Products:
R2C2-cAMP
|
| Hasler et al FASEB J 6:2734-2741 1992 say Kd =1e-7M for type II, 5.6e-8 M for type I. Smith et al PNAS USA 78:3 1591-1595 1981 say that Ka1 is 2.1e7/M which gives a Kd of 47 nM, Kan = 5e8/M or Kd of 2nM. I prefer numbers from Ogreid and Doskeland Febs Lett 129:2 287-292 1981. Their conditions are more physiological. They have figs suggesting time course of complete assoc is < 1 min. | | 7 | cAMP-bind-site-B
2 | PKA
Pathway No. 84 | 54
(uM^-1 s^-1) | 33
(s^-1) | Kd(bf) = 0.6111(uM) | - | Substrate:
R2C2-cAMP
cAMP
Products:
R2C2-cAMP2
|
| For now let us set this to the same Km (1e-7M) as site B1. This gives kf/kb = .7e-7M * 1e6 / (6e5^2) : 1/(6e5^2) = 2e-13:2.77e-12 | | 8 | cAMP-bind-site-A
2 | PKA
Pathway No. 84 | 75
(uM^-1 s^-1) | 32.5
(s^-1) | Kd(bf) = 0.4333(uM) | - | Substrate:
cAMP
R2C2-cAMP3
Products:
R2C2-cAMP4
|
| Cooperativity kicks in, now we have a low Kd for cAMP. | | 9 | Release-C1 | PKA
Pathway No. 84 | 60
(s^-1) | 18
(uM^-1 s^-1) | Kd(cb) = 0.3(uM) | - | Substrate:
R2C2-cAMP4
Products:
PKA-active
R2C-cAMP4
|
| The complex starts to dissociate and release the catalytic subunit C. This has to be fast, as the activation of PKA by cAMP is also fast. | | 10 | Release-C2 | PKA
Pathway No. 84 | 60
(s^-1) | 18
(uM^-1 s^-1) | Kd(cb) = 0.3(uM) | - | Substrate:
R2C-cAMP4
Products:
PKA-active
R2-cAMP4
|
| Second catalytic subunit is now released. | | 11 | RecLigandBinding | Gq
Pathway No. 74 | 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. | | 12 | Ca_act_PLC_g | PLC_g
Pathway No. 79 | 180
(uM^-1 s^-1) | 10
(s^-1) | Kd(bf) = 0.0556(uM) | - | Substrate:
PLC_g
Ca
Products:
Ca.PLC_g
|
| Nice curves from Homma et al JBC 263:14 6592-6598 1988 Fig 5c. The activity falls above 10 uM, but that is too high to reach physiologically anyway, so we'll ignore the higher pts and match the lower ones only. Half-max at 1 uM. But Wahl et al JBC 267:15 10447-10456 1992 have half-max at 56 nM which is what I'll use. | | 13 | Ca_act_PLC_g* | PLC_g
Pathway No. 79 | 12
(uM^-1 s^-1) | 10
(s^-1) | Kd(bf) = 0.8333(uM) | - | Substrate:
Ca
PLC_G*
Products:
Ca.PLC_g*
|
| Again, we refer to Homma et al and Wahl et al, for preference using Wahl et al JBC 267(15):10447-10456 1992. Half-Max of the phosph form is at 316 nM. Use kb of 10 as this is likely to be pretty fast. As we are phosphorylating the Ca-bound form, equils have shifted. kf should now be 2e-5 (Kf = 12) to match the reported half-max. | | 14 | CaM-TR2-Ca2-bind
-Ca | CaM
Pathway No. 81 | 3.6
(uM^-1 s^-1) | 10
(s^-1) | Kd(bf) = 2.7778(uM) | - | Substrate:
CaM-TR2-Ca2
Ca
Products:
CaM-Ca3
|
| Stemmer and Klee 1994 Biochem 33:6859-6866 K3 = 21.5, K4 = 2.8. Assuming that the K4 step happens first, we get kb/kf = 2.8 uM = 1.68e6 so kf =6e-6 assuming kb = 10 | | 15 | CaM-Ca3-bind-Ca | CaM
Pathway No. 81 | 0.465
(uM^-1 s^-1) | 10
(s^-1) | Kd(bf) = 21.5054(uM) | - | Substrate:
CaM-Ca3
Ca
Products:
CaM-Ca4
|
| Use K3 = 21.5 uM here from Stemmer and Klee table 3. Stemmer and Klee 1994 Biochem 33:6859-6866 kb/kf =21.5 * 6e5 so kf = 7.75e-7, kb = 10 | | 16 | PKC-act-by-DAG | PKC
Pathway No. 71 | 0.008
(uM^-1 s^-1) | 8.6348
(s^-1) | Kd(bf) = 1079.377(uM) | - | Substrate:
DAG
PKC-Ca
Products:
PKC-Ca-DAG
|
| Ca.PKC interaction with DAG is modeled by this reaction. Kf based on Shinomura et al PNAS 88 5149-5153 1991 and Schaechter and Benowitz 1993 J Neurosci 13(10):4361 and uses the constraining procedure referred to in the general notes for PKC. | | 17 | CaMKII-bind-CaM | CaMKII
Pathway No. 80 | 49.9998
(uM^-1 s^-1) | 5
(s^-1) | Kd(bf) = 0.1(uM) | - | Substrate:
CaM-Ca4
CaMKII
Products:
CaMKII-CaM
|
| This is tricky. There is some cooperativity here arising from interactions between the subunits of the CAMKII holoenzyme. However, the stoichiometry is 1. Kd = 0.1 uM. Rate is fast (see Hanson et al Neuron 12 943-956 1994) Hanson and Schulman 1992 AnnRev Biochem 61:559-601 give tau for dissoc as 0.2 sec at low Ca, 0.4 at high. Low Ca = 100 nM = physiol. | | 18 | CaM_bind_PDE1 | AC
Pathway No. 85 | 720
(uM^-1 s^-1) | 5
(s^-1) | Kd(bf) = 0.0069(uM) | - | Substrate:
PDE1
CaM-Ca4
Products:
CaM.PDE1
|
| Borisy et al J Neurosci 12(3):915-923 For olf epithelium PDE1, affinity is 7 nM CaM and about 2 uM Ca which is consistent with it binding Ca4.CaM at 7 nM. Assume same for brain. Reaction should be pretty fast. Assume kb = 5/sec. | | 19 | DAG-Ca-PLA2-act | PLA2
Pathway No. 72 | 0.003
(uM^-1 s^-1) | 4
(s^-1) | Kd(bf) = 1333.3333(uM) | - | Substrate:
DAG
PLA2-Ca*
Products:
DAG-Ca-PLA2*
|
| Synergistic activation of PLA2 by Ca and DAG. Based on Leslie and Channon 1990 BBA 1045:261 The Kd is rather large and may reflect the complications in measuring DAG. For this model it is not critical since DAG is held fixed. | | 20 | PKC-Ca-to-memb | PKC
Pathway No. 71 | 1.2705
(s^-1) | 3.5026
(s^-1) | Keq = 2.7569(uM) | 0.21sec | Substrate:
PKC-Ca
Products:
PKC-Ca-memb*
|
| Membrane translocation is a standard step in PKC activation. It also turns out to be necessary to replicate the curves from Schaechter and Benowitz 1993 J Neurosci 13(10):4361 and Shonomura et al 1991 PNAS 88:5149-5153. These rates are constrained by matching the curves in the above papers and by fixing a rather fast (sub-second) tau for PKC activation. |
and 
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