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Molecule Parameter List for PIP2 | The statistics table lists the distribution of a molecule acting either as a substrate, product, enzyme or as a molecule within the network.
The text color of a molecule is highlighted by  color. | | Statistics |
| PIP2 participated as | Molecule | Sum total of | Enzyme | Substrate of an enzyme | Product of an enzyme | Substrate in Reaction | Product in Reaction | | No. of occurrences | 1 | 0 | 0 | 4 | 0 | 0 | 0 |
Accession and Pathway Details | |
| Accession Name | Accession No. | Accession Type | Pathway Link | Synaptic_
Network | 16 | Network |
Shared_Object_Synaptic_Network, PKC, PLA2,
PLCbeta, Gq, MAPK,
Ras, EGFR, Sos,
PLC_g, CaMKII, CaM,
PP1, PP2B, PKA,
AC, CaRegulation | This model is an annotated version of the synaptic signaling network.
The primary reference is Bhalla US and Iyengar R. Science (1999) 283(5400):381-7 but several of the model pathways have been updated.
Bhalla US Biophys J. 2002 Aug;83(2):740-52
Bhalla US J Comput Neurosci. 2002 Jul-Aug;13(1):49-62 |
PIP2 acting as a Molecule in Synaptic_Network Network
| Name | Accession Name | Pathway Name | Initial Conc.
(uM) | Volume
(fL) | Buffered | | PIP2 | Synaptic_
Network
Accession No. : 16 | Shared_Object_
Synaptic_
Network
Pathway No. : 70 | 10 | 1000 | Yes | | PIP2 is a bit troublesome in this model. Its level is well below what it should be based on more recent data. This value is kept in this model to correspond to the Km used in the enzymes. A scale factor of 5-10 in both terms would cancel out but improve the parameter estimate. |
PIP2 acting as a Substrate for an Enzyme in Synaptic_Network Network
| | Enzyme Molecule /
Enzyme Activity | Accession Name | Pathway Name | Km (uM) | kcat (s^-1) | Ratio | Enzyme Type | Reagents | | 1 | PLC-Ca /
PLC-Ca | Synaptic_
Network
Accession No. : 16 | PLCbeta
Pathway No. : 73 | 19.8413 | 10 | 4 | explicit E-S complex | Substrate
PIP2
Product
DAG
IP3
| | | From Sternweis et al Phil Trans R Soc Lond 1992, also matched by Homma et al. Km of 20 is higher than for the Gq bound form, but Vmax is about 1/3 of the Gq form. | | 2 | PLC-Ca-Gq /
PLCb-Ca-Gq | Synaptic_
Network
Accession No. : 16 | PLCbeta
Pathway No. : 73 | 5 | 48 | 4 | explicit E-S complex | Substrate
PIP2
Product
DAG
IP3
| | | From Sternweis et al, Phil Trans R Soc Lond 1992, and the values from other refs eg Homma et al JBC 263(14) pp6592 1988 match. In this model I have rather low values for PIP2. The Km values are low to match. Sternweis mentions a 5 uM Km which is what I use here, but the Homma paper suggests about 20x higher Km, which would also fit with 20x higher PIP2. So that parameter, though it is off, cancels out and the overall rate would be the same. Vmax is about 23 umol/min/mg at high Ca from Sternweis or about 60/sec. This model value is a little lower than that. | | 3 | Ca.PLC_g /
PIP2_hydrolysis | Synaptic_
Network
Accession No. : 16 | PLC_g
Pathway No. : 79 | 97.2222 | 14 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | Substrate
PIP2
Product
DAG
IP3
| | | Wahl et al JBC 267(15) 10447-10456 1992. Homma et al JBC 263:14 1988 pp 6592. These parms are the Ca-stimulated form. This is close to Wahl's figure 7, which I am using as reference. Also see Nakanishi et al Biochem J 256 453-459 1998, Nishibe et al Science 250 :1253-1256 This model uses a rather low PIP2 of 10 uM. | | 4 | Ca.PLC_g* /
PIP2_hydrolysis | Synaptic_
Network
Accession No. : 16 | PLC_g
Pathway No. : 79 | 19.7917 | 57 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | Substrate
PIP2
Product
DAG
IP3
| | | Mainly Homma et al JBC 263:14 1988 pp 6592. These parms are the Ca-stimulated form. Wahl et al JBC 267:15 10447-10456 1992 say that the tyrosine phosphorylated form has 7X higher affinity for substrate than control. The PIP2 levels in this model are rather low, at 10 uM. |
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