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Reaction List for pathway IP4-system (Pathway Number 154) | | 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 |
5kinase | kf
(s^-1) | 0.006
(uM^-1 s^-1) | Kd(cb) = 0.086(uM) | - | IP3-56Kcmplx
| IP4(1345)
IP3-56K_IP4-1K
| | | Kf = 0.274 times Vmax of IP3 56-K as product ratio of Ins(1345)P4 : Ins(1346)P4 is 1 : 2.3-5 from Wilson and Majerus, JBC 271; 1996 Kb ascertained from dG calculations for equilibrium conditions., for a dG = -10 kJ/mol Also enzyme reversibility reported in Ho et al, Curr Biol 2002, 12: 1-20 | | 2 |
6kinase | kf
(s^-1) | 0
(uM^-1 s^-1) | - | - | IP3-56Kcmplx
| IP4(1346)
IP3-56K_IP4-1K
| | | Kf = Vmax for IP3 56-K from Yang and Shears, Biochem J 2000; 351:551-555 Enzyme reversibility reported in Ho et al, Curr Biol 2002, 12: 1-20. But backflow calculations do not show that Kb needs to be incorporated | | 3 |
IP3-Kcmplx-on | kf
(uM^-1 s^-1) | 1.024
(s^-1) | Kd(bf) = 0.24(uM) | - | IP3(134)
IP3-56K_IP4-1K
| IP3-56Kcmplx
| | | Kf and Kb are equivalent to k1 and k2 for InsP3 56-K, calculated from enzyme Km and Vmax: Yang and Shears, BiochemJ 2000, 351: 551-555 | | 4 |
ip4-1k-off | kf
(s^-1) | 0.056
(uM^-1 s^-1) | Kd(cb) = 0.0897(uM) | - | ip4_1k_cmplx
| IP5(13456)
IP3-56K_IP4-1K
| | | Kf = enzyme Vmax : Yang and Shears, Biochem J 2000, 351, 551-5. Kb ascertained from dG calculations for equilibrium product substrate conditions. Ho et al, Curr Biol 2002, 12: 1-20 report a Vmax for reverse reaction of 0.0656 /sec. But this cannot be exactly incorporated unless Km for InsP5 is also known. Simulations show that incorporation of this reverse reaction can maintain basal InsP4 levels but cannot achieve the stimulated InsP4 levels shown in Ho et al. Hence the separate InsP5 1pase is retained. | | 5 |
ip4-1k-on | kf
(uM^-1 s^-1) | 2.496
(s^-1) | Kd(bf) = 0.08(uM) | - | IP4(3456)
IP3-56K_IP4-1K
| ip4_1k_cmplx
| | | Rates derives from enzyme Km and Vmax values: Yang and Shears, Biochem J 2000, 351: 551-555. | | 6 |
ip4-3k-off | kf
(s^-1) | 0.2687
(uM^-1 s^-1) | Kd(cb) = 0.0625(uM) | - | ip4_3k_cmplx
| IP4-3K
IP5(13456)
| | | Kf = Vmax for enzyme: Stephens et al, Biochem J 249; 1988. Kb ascertained from dG calculations for equilibrium conditions. | | 7 |
ip4-3k-on | kf
(uM^-1 s^-1) | 17.2
(s^-1) | Kd(bf) = 0.32(uM) | - | IP4(1456)
IP4-3K
| ip4_3k_cmplx
| | | Rates derived from Km for enzyme: Stephens et al, Biochem J 249; 1988. | | 8 |
ip4-5K | kf
(s^-1) | 0.003
(s^-1) | Keq = 0.02(uM) | 6.536sec | IP4(1346)
| IP5(13456)
| | | Kf based on basal levels of Ins(1346)P4 Kb obtained from dG calculations for equilibrium product substrate conditions. | | 9 |
ip4-6pase | kf
(s^-1) | 0
(s^-1) | - | - | IP4(1456)
| IP3(145)
| | | this step is essential to maintain flux around the network, rate adjusted accordingly | | 10 |
ip5_1pase | kf
(s^-1) | 0
(s^-1) | - | - | IP5(13456)
| IP4(3456)
| | | InsP5 1-phosphatase Reaction is necessary to generate the flux of Ins(3456)P4 seen physiologically (Ho et al Curr Biol 2002, 12:1-20), although the IP4-1K/pase can maintain basal levels of this InsP4. | | 11 |
ip5_3pase | kf
(s^-1) | 0
(s^-1) | - | - | IP5(13456)
| IP4(1456)
| | | Ins(13456)P5 3-phosphatase from Nogimori et al, JBC 266; 1991 Backflux from the reversible InsP4 3-kinase is not sufficient to maintain Ins(1456)P4 levels. Hence this reaction is necessary. This reaction also maintains the flux in the network. |
Pathway Details Molecule List Enzyme List Reaction List
| Database compilation and code copyright (C) 2022, Upinder S. Bhalla and NCBS/TIFR
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