Table 4.

Estimation of the receptor:CheA mole ratio in chemotactic signaling complexes

Receptor modification	$V_{\text{sat}}^{\text{apo}}$ for saturating CheA at 2.0 μM receptora	$V_{\text{sat}}^{\text{apo}}$ for saturating receptor at 0.5 μM CheAb	Calculated receptor:CheA mole ratioc
QEEE	0.6 ± 0.1	1.0 ± 0.2	6.7 ± 1.7
QEQE	1.7 ± 0.2	2.3 ± 0.4	5.4 ± 1.1
QQQQ	4.1 ± 0.3	5.4 ± 0.4	5.3 ± 0.5
G278V/QQQQ	8.0 ± 0.5	10.3 ± 0.9	5.2 ± 0.6

^aThe $V_{\text{sat}}^{\text{apo}}$ for saturating CheA was obtained as shown in Figure 6(A). The soluble chemotaxis components were covaried at a relative CheA to CheW to CheY ratio of 4:1:20, while the receptor concentration was fixed at 2.0 μM. Under these conditions, the CheW and CheY concentrations were always saturating, and the receptor concentration limited the maximum number of signaling complexes that could be formed. All concentrations are monomeric, and all receptors are assumed to be accessible to complex assembly.

^bThe $V_{\text{sat}}^{\text{apo}}$ for saturating receptor was obtained as shown in Figure 6(B). The soluble chemotaxis components were fixed at a relative CheA to CheW to CheY ratio of 4:1:20, with a total CheA monomer concentration of 0.5 μM. Under these conditions, the CheW and CheY concentrations were always saturating, and the CheA concentration limited the maximum number of signaling complexes that could be formed. All concentrations are monomeric, and all receptors are assumed to be accessible to complex assembly.

^cEstimated receptor to CheA mole ratio. To obtain this value, the concentration of receptor needed to increase the $V_{\text{sat}}^{\text{apo}}$ value of column 2 to match the $V_{\text{sat}}^{\text{apo}}$ value of column 3 is calculated. Subsequently, this receptor concentration is divided by the CheA concentration from column 3 (0.5 μM) to give the calculated receptor to CheA mole ratio of the fully assembled signaling complex.