| |
Reaction
Name | Pathway Name /
Pathway No. | Kf | Kb | Kd | tau | Reagents |
| 1 | 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 | | 2 | 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. | | 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.
indicates that ordering is done according to ascending or descending order.