| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | Ca-bind-to-Trans
p | CaRegulation
Pathway No. 86 | 3600
(uM^-2 s^-1) | 144
(s^-1) | Kd(bf) = 0.04(uM) | - | Substrate:
Ca_intracell
Ca_intracell
CaTransp
Products:
CaTransp-2Ca
|
| Rates from Lauffenberger and Linderman 1993 Receptors pg 200. Kd = KCa2 = 0.2 uM. | | 2 | CaTraspATPase | CaRegulation
Pathway No. 86 | 25
(s^-1) | 0
(#^-2 s^-1) | Not applicable** | - | Substrate:
CaTransp-2Ca
Products:
CaTransp
Ca-sequester
Ca-sequester
|
| kCa3 = 2 * Ca transporter rate since each step has 2 Ca++. = 0.5 uM/sec from Lauffenburger and Linderman 1993 Receptors pg 200. The amount of the activated transporter is about 0.01 uM = 6e3 #. from runs. So 0.01uM * kf * 2 = 0.5 uM/sec (no back reaction) so kf = 25, kb = 0 Alternatively, 6e3 * kf = 0.25 * 6e5, giving the same kf | | 3 | IP3Rbind | CaRegulation
Pathway No. 86 | 0.05
(uM^-3 s^-1) | 1
(s^-1) | Kd(af) = 2.7144(uM) | - | Substrate:
IP3R
IP3
IP3
IP3
Products:
IP3R*
|
| Based on Lauffenburger and Linderman 1993 Receptors page 200. The binding of IP3 in this reaction has a Hill coeff of 3. The eqns of Mahama and Linderman (cited in the book as 1993 a) are equivalent to the binding all occurring in a single step, so that is how I am doing it in this version. Their Ki1 is 0.07 uM. Lots of other data sources: Ramos-Franco et al 1998 Biophys J 75:834-839 have Ca sensitivity curves. At 250 nM free Ca, the EC50 for type 1 is 58 nM and type 2 is 194 nM. Type 3 would be about 2 uM according to Newton et al 1994 JBC 268(46):28613-28619 For the purposes of this model we use a Kd of 2.7 uM which is high but may be OK at low calcium. The details of Ca interaction with the IP3R are not included in this model. | | 4 | inactivate_cap_
Ca | CaRegulation
Pathway No. 86 | 0
(#^-2 s^-1) | 1
(s^-1) | Not applicable** | - | Substrate:
Ca-sequester
Ca-sequester
capacitive_Ca_
entry*
Products:
inact_cap_entry
|
| The Kd is set to about 3 uM, so that at resting Ca the capacitive Ca entry is almost blocked. A 2nd order response makes the response steep. |
** This is a trasport reation between compartments of different volumes. Therefore Kd is not applicable. Please Note Kf, Kb units are in number of molecules instead of concentration
and 
color.
