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Reaction List for pathway CaRegulation (Pathway Number 86)

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 reactions is not considered.
  Name KfKbKdtauSubstrateProduct
1 Ca-bind-to-Trans
p		3600
(uM^-2 s^-1)		144
(s^-1)		Kd(bf) = 0.04(uM)-Ca_intracell
Ca_intracell
CaTransp
CaTransp-2Ca
  Rates from Lauffenberger and Linderman 1993 Receptors pg 200. Kd = KCa2 = 0.2 uM.
2 CaTraspATPase25
(s^-1)		0
(#^-2 s^-1)		Not applicable**-CaTransp-2Ca
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 inactivate_cap_
Ca		0
(#^-2 s^-1)		1
(s^-1)		Not applicable**-Ca-sequester
Ca-sequester
  • capacitive_Ca_
    entry*
    		• 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.
    4 IP3Rbind0.05
    (uM^-3 s^-1)    		1
    (s^-1)    		Kd(af) = 2.7144(uM)-IP3R
    IP3
    IP3
    IP3
    		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.
    Pathway DetailMolecule ListEnzyme ListReaction List