| | Molecule Name/
Site Name | Km (uM) | kcat (1/s) | Ratio
(k2/k3) | Enzyme Type | Substrate | Product |
| 1 |
Enzyme Activity:
CaM.PDE1
Enzyme Molecule:
CaM.PDE1 | 39.6825 | 10 | 4 | explicit E-S complex | cAMP
| AMP
|
| | From Conti et al 1995 Biochem 34:7979-7987 the stimulated Vmax is ~10umol/min/mg in presence of lots of CaM. This works out to about 10/sec. Affinity is low, 40 uM. |
| 2 |
Enzyme Activity:
kenz
Enzyme Molecule:
AC1-CaM | 20 | 18 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | ATP
| cAMP
|
| | Vmax is assumed to be the same as that for the Gs-stimulated form. The rates are from: Smigel 1986 JBC 261(4):1976-1982 who has 8.27 umol/min/mg with forskolin stimulated AC. Tang et al JBC 266(13):8595-8603 have an almost identical Vmax of 8 umol/min/mg. This comes to a Vmax of 18/sec. The Km is pretty immaterial since the vast excess of ATP means that the enzyme will normally be saturated. This is a pretty fast enzyme. Note that the saturation of the enzyme means that the regulatory reactions have to involve the complex rather than the free enzyme. |
| 3 |
Enzyme Activity:
kenz
Enzyme Molecule:
AC2* | 20.1149 | 7 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | ATP
| cAMP
|
| | The Vmax is scaled down to 7/sec from the Gs-stimulated form. This is constrained because we have a measure of basal activity due to basal phosphorylation by PKC. Two papers measure activation of AC2 by phosphorylation without Gs: Jacobowitz et al JBC 268(6):3829-3832 (Stim 3x) and Yoshimura and Cooper 1993 JBC 26(7):4604-4607 (Stim 9x). The conditions are somewhat different in the two cases. The reference maximally stimulated Vmax is 18/sec from Smigel 1986 JBC 261(4):1976-1982 who has 8.27 umol/min/mg with forskolin stimulated AC. Tang et al JBC 266(13):8595-8603 have an almost identical Vmax of 8 umol/min/mg. This comes to a Vmax of 18/sec. The Km is pretty immaterial since the vast excess of ATP means that the enzyme will normally be saturated. This is a pretty fast enzyme. Note that the saturation of the enzyme means that the regulatory reactions have to involve the complex rather than the free enzyme. |
| 4 |
Enzyme Activity:
kenz
Enzyme Molecule:
AC2-Gs | 20 | 18 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | ATP
| cAMP
|
| | Vmax is assumed to be the same as for AC1. This is consistent since there is a good match between the mixture of ACs tested by Smigel 1986 JBC 261(4):1976-1982 who has 8.27 umol/min/mg with forskolin stimulated AC. Tang et al JBC 266(13):8595-8603 have an almost identical Vmax of 8 umol/min/mg for AC1. This comes to a Vmax of 18/sec. The Km is pretty immaterial since the vast excess of ATP means that the enzyme will normally be saturated. This is a pretty fast enzyme. Note that the saturation of the enzyme means that the regulatory reactions have to involve the complex rather than the free enzyme. |
| 5 |
Enzyme Activity:
kenz
Enzyme Molecule:
AC1-Gs | 20 | 18 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | ATP
| cAMP
|
| | Vmax is from Smigel 1986 JBC 261(4):1976-1982 who has 8.27 umol/min/mg with forskolin stimulated AC. Tang et al JBC 266(13):8595-8603 have an almost identical Vmax of 8 umol/min/mg. This comes to a Vmax of 18/sec. The Km is pretty immaterial since the vast excess of ATP means that the enzyme will normally be saturated. This is a pretty fast enzyme. Note that the saturation of the enzyme means that the regulatory reactions have to involve the complex rather than the free enzyme. |
| 6 |
Enzyme Activity:
kenz
Enzyme Molecule:
AC2*-Gs | 60 | 54 | 4 | Classical Michaelis-Menten
V = Etot.S.Kcat/Km+S | ATP
| cAMP
|
| | The Km is higher here but it is still well below the level of ATP so the enzyme remains saturated. The Vmax is 3x higher than the reference forskolin stimulated form. This scale factor is a compromise between the 2x rise reported by Jacobowitz et al JBC 268(6): 3829-3832 and the 9x rise reported by Yoshimura and Cooper 1993 JBC 268(7):4604-4607. The reference Vmax is from Smigel 1986 JBC 261(4):1976-1982 who has 8.27 umol/min/mg with forskolin stimulated AC. Tang et al JBC 266(13):8595-8603 have an almost identical Vmax of 8 umol/min/mg. This comes to a Vmax of 18/sec. The Km is pretty immaterial since the vast excess of ATP means that the enzyme will normally be saturated. This is a pretty fast enzyme. Note that the saturation of the enzyme means that the regulatory reactions have to involve the complex rather than the free enzyme. |
| 7 |
Enzyme Activity:
PDE
Enzyme Molecule:
cAMP-PDE | 19.8413 | 10 | 4 | explicit E-S complex | cAMP
| AMP
|
| | Best rates are from Conti et al Biochem 34 7979-7987 1995. Though these are for the Sertoli cell form, it looks like they carry nicely into alternatively spliced brain form. See Sette et al JBC 269:28 18271-18274 Borisy et al J Neurosci 12(3):915-923 also have estimates with a Km of 40 uM specifically for brain PDE. The Vmax is very low and it looks like the purification is not good. Combining this with data from the Conti paper and the Sette paper, it looks like a fair compromise is Km ~20 uM, Vmax est ~ 10 umol/min/mg or about 10/sec. |
| 8 |
Enzyme Activity:
PDE*
Enzyme Molecule:
cAMP-PDE* | 19.8413 | 20 | 4 | explicit E-S complex | cAMP
| AMP
|
| | This form has about twice the activity of the unphosphorylated form. See Sette et al JBC 269:28 18271-18274 1994. We'll ignore cGMP effects for now. The Vmax is therefore scaled to twice the value used in the unstimulated PDE enzyme. |
| 9 |
Enzyme Activity:
PDE1
Enzyme Molecule:
PDE1 | 39.7 | 1.667 | 4.0012 | explicit E-S complex | cAMP
| AMP
|
| | From Borisy et al J Neurosci 12(3):915-923 the basal rate goes up 6x with Ca stimulation. Km = 40. The stimulated Vmax in this paper is very low. But Conti et al 1994 Biochem 34:7979-7987 report a 2000x purified form which has a stimulated Vmax of 10 umol/min/mg or about 10/sec (given that the mol wt is around 65KDa.). Here we use a Vmax = 1/6 of the CaM stim form. |
