Table 1.
Apparent weight and stalling rpm for wild-type and myosin knockout mutants in Dictyostelium
| Cell lines* | NC4 | Ax3 | HS1 | A5 |
|---|---|---|---|---|
| Calculation of reduced mass of amoebae | ||||
| Volume† (×10−10 cm3) | 3.78 ± 1.44 | 4.87 ± 1.80 | 4.26 ± 1.34 | 4.87 ± 1.69 |
| Density‡ (gram/cm3) | 1.066 | 1.065 | 1.063 | 1.063 |
| ΔMass§ (×10−11 gram) | 2.31 ± 0.70 | 2.92 ± 0.70 | 2.47 ± 0.78 | 2.82 ± 0.98 |
| Apparent weight at stalling rpm¶ | ||||
| Maximum rotation, rpm | >11,700 | 6,400 | 3,500 | 3,400 |
| Stalling acceleration (×g) | >11,465 | 3,431 | 1,025 | 968 |
| Apparent weight at Stall‖ (× 103 pN) | >2.59 ± 0.78 | 0.99 ± 0.24 | 0.25 ± 0.08 | 0.27 ± 0.09 |
The apparent weight was calculated by multiplying the amoeba's reduced mass and the stalling acceleration. The stalling acceleration was calculated from the rpm beyond which the amoebae were unable to crawl centripetally and the distance (7.5 cm) between the center of the rotor to the center of the observation chamber.
NC4: wild type (12), Ax3: axenic strain (13, 14), HS1: myosin II knockout (mhcA−) (15), A5; triple knockout (mhcA−/myoIA−/myoIB−).
Calculated from measurements of radii of 200 cells each; each cell was assumed to be a 5-μm-high disk.
Apparent cell density (δ) was determined as isopycnic density (17).
ΔMass; reduced mass = (cell density − medium density) × cell volume. Medium density of the standard buffer (ρo) was 1.005 gram/cm3 as measured with an Ostwald's pycnometer (21).
(ΔMass) × (stalling acceleration); standard deviation, each based on measurements of radii of 200 cells.