Primary kinetic characterization of recombinant full-length human PDE4A expressed in COS cells. Reports Km for cAMP hydrolysis directly from Michaelis-Menten analysis. This is the best available primary source for PDE4_KM in the h05 model in absence of a hair-cell-specific PDE4 kinetics paper.
Key finding
Full-length PDE4A (HSPDE4A4B): Km = 4.8 µM for cAMP. Truncated core: Km = 3.3 µM. Both values support the h05 model PDE4_KM_NM = 4000 nM (4 µM). Vmax was not explicitly tabulated but relative activities reported. Rolipram IC50: 0.195 µM (particulate) vs 1.6 µM (cytosolic).
Numbers that matter
| Parameter | Value | Units | Conditions | Notes |
|---|---|---|---|---|
| Km cAMP (full-length PDE4A) | 4.8 | µM | Recombinant in COS cells | Direct Michaelis-Menten |
| Km cAMP (truncated core PDE4A) | 3.3 | µM | Recombinant in COS cells | Core catalytic domain only |
| Vmax | not tabulated | — | — | Relative activity reported but not absolute Vmax |
| PDE4_KM_NM (h05 model) | 4000 | nM (4 µM) | — | Consistent with Owens 1997 full-length value |
Limitations
- COS cell expression system; may differ from native PDE4 in cochlear hair cells.
- PDE4 isoform expressed in OHC is not established — no cochlear-specific PDE4 isoform kinetics available.
- Vmax not directly measured; h05 PDE4_VMAX is model-fitted and unsourced.
Connections
[source]calcium-oscillation — primary Km measurement replacing “Houslay 2010” phantom[see-also]2003-houslay-adams-pde4-review[applies]STRC Calcium Oscillation Acoustic Therapy