TABLE 1:
Contribution of GCA and sGC to guanylyl cyclase activity and chemoattractant-stimulated cGMP response.
| Condition | GCA (% of sum) | sGC (% of sum) |
|---|---|---|
| 1 h starved | ||
| Enzyme activity (pmol/min per mg) | 5.8 ± 1.7 (35%) | 11.0 ± 1.1 (65%) |
| cGMP response by folate (pmol/107 cells) | 1.8 ± 0.4 (18%) | 8.5 ± 1.5 (82%) |
| 5 h starved | ||
| Enzyme activity (pmol/min per mg) | 2.6 ± 0.6 (13%) | 17.1 ± 2.2 (87%) |
| cGMP response by cAMP (pmol/107 cells) | 1.5 ± 1.2 (7%) | 18.7 ± 3.4 (93%) |
sgc-null and gca-null cells express only GCA or only sGC, respectively. Cells were starved for 1 h or 5 h to make them optimally sensitive to folate and cAMP, respectively. Guanylyl cyclase enzyme activity was measured in cell lysates using Mg2+-GTP as substrate. Intact cells were stimulated with either 1 μM folate or 0.1 μM cAMP, and samples for cGMP determination were collected at 0 and 10 s after stimulation; the increase of cGMP levels at 10 s after stimulation is shown. Data are means and SD of three independent experiments, each with triplicate determinations. The relative importance of GCA and sGC in enzyme activity and cGMP responses is calculated as percentage of the sum of the activities.