| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | Act-PLC-Ca | PLCbeta
Pathway No. 73 | 3
(uM^-1 s^-1) | 1
(s^-1) | Kd(bf) = 0.3333(uM) | - | Substrate:
Ca
PLC
Products:
PLC-Ca
|
| Affinity for Ca = 1uM without AlF, 0.1 with: from Smrcka et al science 251 pp 804-807 1991 Assigned affinity to a Kd of 0.333 to maintain detailed balance. | | 2 | Act-PLC-by-Gq | PLCbeta
Pathway No. 73 | 25.2
(uM^-1 s^-1) | 1
(s^-1) | Kd(bf) = 0.0397(uM) | - | Substrate:
G*GTP
PLC-Ca
Products:
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 | | 3 | PLC-bind-Gq | PLCbeta
Pathway No. 73 | 2.52
(uM^-1 s^-1) | 1
(s^-1) | Kd(bf) = 0.3968(uM) | - | Substrate:
PLC
G*GTP
Products:
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. | | 4 | PLC-Gq-bind-Ca | PLCbeta
Pathway No. 73 | 30
(uM^-1 s^-1) | 1
(s^-1) | Kd(bf) = 0.0333(uM) | - | Substrate:
Ca
PLC-Gq
Products:
PLC-Ca-Gq
|
| this step has a high affinity of 0.1 uM for Ca, from Smrcka et al 1991 Science 251:804-807 so kf /kb = 1/6e4 = 1.666e-5:1. See the Act-PLC-by-Gq reaction. Raised kf to 5e-5 based on match to conc-eff curves from Smrcka et al. | | 5 | Degrade-IP3 | PLCbeta
Pathway No. 73 | 2.5
(s^-1) | 0
(s^-1) | - | - | Substrate:
IP3
Products:
Inositol
|
| The enzyme is IP3 5-phosphomonesterase. about 45K. Actual products are Ins(1,4)P2, and cIns(1:2,4,5)P3. review in Majerus et al Science 234 1519-1526, 1986. Meyer and Stryer 1988 PNAS 85:5051-5055 est decay of IP3 at 1-3/sec | | 6 | Degrade-DAG | PLCbeta
Pathway No. 73 | 0.15
(s^-1) | 0
(s^-1) | Not applicable** | - | Substrate:
DAG
Products:
PC
|
| Rates based on basal and activation levels of DAG. | | 7 | Inact-PLC-Gq | PLCbeta
Pathway No. 73 | 0.0133
(s^-1) | 0
(uM^-1 s^-1) | - | - | Substrate:
PLC-Ca-Gq
Products:
G*GDP
PLC-Ca
|
| This process is assumed to be directly caused by the inactivation of the G*GTP to G*GDP. Hence, kf = .013 /sec = 0.8/min, same as the rate for Inact-G. kb = 0 since this is irreversible. We may be interested in studying the role of PLC as a GAP. If so, the kf would be faster here than in Inact-G |
and 
color.
