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Accession Type:
Network
MAPK-bistability
-fig1c
Shared_Object_
MAPK-bistability
-fig1c
 Molecule
 Enzyme
 Reaction
Sos
PKC
MAPK
PLA2
Ras
PDGFR

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Reaction List for pathway Shared_Object_MAPK-bistability-fig1c (Pathway Number 179)

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 KfKbKdtauSubstrateProduct
1 Ras-act-craf60
(uM^-1 s^-1)
0.5
(s^-1)
Kd(bf) = 0.0083(uM)-craf-1*
GTP-Ras
Raf*-GTP-Ras
  Assume binding is fast and limited only by available Ras*. So kf = kb/[craf-1] If kb is 1/sec, then kf = 1/0.2 uM = 1/(0.2 * 6e5) = 8.3e-6 Later: Raise it by 10 X to about 1e-4, giving a Kf of 60 for Kb of 0.5 and a tau of approx 2 sec. Based on: Hallberg et al JBC 269:6 3913-3916 1994, 3% of cellular Raf is complexed with Ras. This step needed to memb-anchor and activate Raf: Leevers et al Nature 369 411-414. Also see Koide et al 1993 PNAS USA 90(18):8683-8686
2 Ras-act-unphosph
-raf
6
(uM^-1 s^-1)
1
(s^-1)
Kd(bf) = 0.1667(uM)-craf-1
GTP-Ras
RGR
  Based on rates of Ras-act-craf which has Kf=60, Kb= 0.5. This reaction was introduced to account for the PKC-independent activation of MAPK. This reac should have less affinity but similar tau as compared to the Ras-cat-craf, since the phosphorylated Raf form has a greater effect on MAPK.


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