Table 1.

Some examples of ultrasensitivity in signal transduction

Stimulus	Response	Effective Hill Exponent	Experimental System	Reference
Acetylcholine	Nicotinic cholinergic receptor conductance	1.3	Chicken neuronal homomeric α7 receptors	[23]
Delta (in trans only)	Notch production	1.7	CHO cells	[24]
Mos	MEK1	1.7	Xenopus laevis oocyte extracts	[25]
Phosphorylase kinase/phosphatase	Glycogen phosphorylase	2	Reconstituted mammalian muscle enzymes	[21]
RsbQP	σ B	2.1	Bacillus subtilis	[26]
AICAR	AMPK	2.5	Rat INS-1 cells	[27]
Ca2+	Calmodulin-dependent cAMP phosphodiesterase	2.7*	Purified beef heart proteins	[28]
IP3	Calcium release	3	Permeablized rat basophilic leukemia cells	[29]
Cdk1	Wee1A	3.5	Xenopus laevis egg extracts	[30]
Anisomycin	Jnk	3 - 10	HeLa, HEK293, and Jurkat cells	[31]
Sorbitol	Jnk	4 - 9	HeLa, HEK293, and Jurkat cells	[31]
Mos	Erk2	5	Xenopus laevis oocytes	[25]
Cln2	Cln2 synthesis	5	S. cerevisiae	[32]
KinA	σE and σF	10	Bacillus subtilis	[33]
CheY-P	Flagellar motor output	~10 - 20	Escherichia coli	[34-36]
Cdk1	Cdc25C	11	Xenopus laevis egg extracts	[37]
Delta (cis and trans)	Notch production	12	CHO cells	[24]
Cdk1	APC/CCdc20	≥ 17	Xenopus laevis egg extracts and embryos	[38, 39]
Yan	ERK	Not determined	Drosophila embryos	[22]

^*Our estimate based on the data in Fig 3 from [28].