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Accession Type:
Pathway
CO_activation_
of_GC
sGC
 Molecule
 Enzyme
 Reaction

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Reaction List for pathway sGC (Pathway Number 140)

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 CObindsGCakf
(uM^-1 s^-1)
28
(s^-1)
Kd(bf) = 233.3333(uM)-sGC
CO
GC6-CO
  This gives rise to the six co-ordinate carboxy GC. Kharitonov et al., 1995, PNAS, 92:2568-2571 report CO association and dissociation rates at 1.2e5 /M/sec and 28 /sec respectively. Kharitonov et al., 1999, Biochemistry, 38(33):10699-10706 report Ka at 7.86 +- 0.50 /mM.
2 CObindsHbO2kf
(uM^-1 s^-1)
0.0078
(s^-1)
Kd(bf) = 0.0459(uM)-dissoCO
Ery_HbO2
COHb
  CO binds to hemoglobin, predominantly the erythrocyte associated hemoglobin. The affinity of hemoglobin for CO is 200-250 times that of oxygen, while relative affinities of heme proteins (myoglobin), cytochrome oxidase and cytochrome P-450 for CO are much lower. CO binds reversibly to hemoglobin to form Carboxy hemoglobin, (COHb) from which CO is exhaled through the lungs. Primary source for rates, Migita et al., JBC, 1998, 273(2): 945-949, and refs cited in their paper.
3 Kkf
(s^-1)
0
(s^-1)
--GC6-CO
GC5_CO
  The transition from six co-ordinate to the five co-ordinate carboxy GC. CO dissociation rate for 6 coord sp for heme is 0.95 /sec. (Kharitonov et al., 1995, PNAS, 92:2568-2571)
4 kkf
(s^-1)
0
(s^-1)
--GC5_CO
dissoCO
  The dissociation of CO from the active five co-ordinate GC. rate from Kharitonov et al., PNAS, 1995, 92:2568-2571. Further justification include the fact that Soret absorption spectrum of GC-NO suggesting almost complete sonversion to five co-ordinate species. So, assuming that the five co-ord species is more active than the basal form, irrespective of the Ligand, the percentage of five co-ordinate intermediate induced by CO was calculated to be 3% to 1.5%.(Kharitonov et al., 1995, PNAS) using mean value, ~ 2 +- 1 %, and kobs = 28/sec, k = 1*10^3/sec. (Kharitonov et al., PNAS, 1995, 92:2568-2571)


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