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Molecule Parameter List for G*GTP

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

G*GTP 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	0	0	3	2

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

G*GTP acting as a Molecule in  Synaptic_Network Network

Name	Accession Name	Pathway Name	Initial Conc. (uM)	Volume (fL)	Buffered
G*GTP	Synaptic_ Network Accession No. : 16	Shared_Object_ Synaptic_ Network Pathway No. : 70	0	1000	No
Activated G protein. Berstein et al indicate that about 20-40% of the total Gq alpha should bind GTP at steady stimulus.

G*GTP acting as a Substrate in a reaction in  Synaptic_Network Network

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 reaction are not consider.

	Name	Accession Name	Pathway Name	Kf	Kb	Kd	tau	Reagents
1	Act-PLC-by-Gq	Synaptic_ Network Accession No. : 16	PLCbeta Pathway No. : 73	25.2 (uM^-1 s^-1)	1 (s^-1)	Kd(bf) = 0.0397(uM)	-	Substrate G*GTP PLC-Ca Product PLC-Ca-Gq
	Affinity for Gq is > 20 nM (Smrcka et al Science251 804-807 1991) so [Gq].kf = kb so 40nM * 6e5 = kb/kf = 24e3 so kf = 4.2e-5, kb =1
2	PLC-bind-Gq	Synaptic_ Network Accession No. : 16	PLCbeta Pathway No. : 73	2.52 (uM^-1 s^-1)	1 (s^-1)	Kd(bf) = 0.3968(uM)	-	Substrate G*GTP PLC Product PLC-Gq
	this binding does not produce active PLC. This step was needed to implement the described (Smrcka et al) increase in affinity for Ca by PLC once Gq was bound. The kinetics are the same as the binding step for Ca-PLC to Gq. Kd is constrained by detailed balance.
3	Inact-G	Synaptic_ Network Accession No. : 16	Gq Pathway No. : 74	0.0133 (s^-1)	0 (s^-1)	-	-	Substrate G*GTP Product G*GDP
	From Berstein et al JBC 267:12 8081-8088 1992, kcat for GTPase activity of Gq is only 0.8/min.

G*GTP acting as a Product in a reaction in  Synaptic_Network Network

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 reaction are not consider.

	Name	Accession Name	Pathway Name	Kf	Kb	Kd	tau	Reagents
1	Basal-Act-G	Synaptic_ Network Accession No. : 16	Gq Pathway No. : 74	0.0001 (s^-1)	0 (uM^-1 s^-1)	-	-	Substrate G-GDP Product BetaGamma G*GTP
	This is the basal exchange of GTP for GDP. So slow as to be nearly negligible.
2	Activate-Gq	Synaptic_ Network Accession No. : 16	Gq Pathway No. : 74	0.01 (s^-1)	0 (uM^-2 s^-1)	-	-	Substrate Rec-Glu-Gq Product BetaGamma G*GTP Rec-Glu
	This reaction is the critical one for activation of Gq. It probably encapsulates multiple steps. In this approximation the receptor-ligand- Gprotein complex splits up into GTP.Galpha, rec.ligand complex, and Gbetagamma. There is a hidden step of exchange of GDP for GTP. The reaction does not take these into account since it is assumed that both GTP and GDP levels are tightly regulated by metabolic control. 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.