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Comment
. 2003 Feb;84(2 Pt 1):1410-1.
doi: 10.1016/S0006-3495(03)74955-8.

Amplifying signal transduction specificity without multiple phosphorylation

Hong Qian
Comment

Amplifying signal transduction specificity without multiple phosphorylation

Hong Qian. Biophys J. 2003 Feb.
No abstract available

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Figures

FIGURE 1
FIGURE 1
A kinetic schematics for PdPC. E1 and E2 represent kinase and phosphatase. The substrate, protein W, is phosphorylated by the kinase to become W*, which in turn is dephosphorylated by E2. A complete reaction cycle hydrolyzes one formula image Hence, formula image where formula image is the phosphorylation potential. Both enzymatic reactions are nearly irreversible: formula image Let formula image be the total substrate concentration neglecting the small amount of enzyme-substrate complexes, E1T and E2T the total enzyme concentrations for E1 and E2. Goldbeter and Koshland (1981) showed that the number of model parameters can be reduced, with nondimensionalization, to four key parameters: formula image, formula image are the Michaelis-Menten constants, and formula image, formula image are maximal velocities, for E1 and E2 respectively. formula image is a measure of the strength of stimuli/inhibition. K1 and K2 are directly related to the affinity of the enzymes to their respective substrates.
FIGURE 2
FIGURE 2
The amplified specificity of PdPC with single phosphorylation when phosphorylation potential formula image (A) The steady-state level of activation, W*, as function of K1, the dissociation constant between kinase E1 and its protein substrate W. K2 is kept at 0.01. The thick solid, dashed, and dotted lines are for σ = 10, 1, and 0.9 respectively. The first two curves have Hill coefficients of 2 and 1. Calculations for σ > 10 are indistinguishable from the solid line. For comparison, the thin solid line is for nonamplified specificity: formula image (B) Steady-state W* as function of K2, the dissociation constant between phosphatase E2 and its protein substrate W*. K1 is kept at 0.01. The thick solid, dashed, and dotted lines are for σ = 0.1, 1, and 1.1, respectively. Calculations for σ < 0.1 are indistinguishable from the solid line. Again, the thin solid line is for nonamplified specificity with Hill coefficient 1: formula image
FIGURE 2
FIGURE 2
The amplified specificity of PdPC with single phosphorylation when phosphorylation potential formula image (A) The steady-state level of activation, W*, as function of K1, the dissociation constant between kinase E1 and its protein substrate W. K2 is kept at 0.01. The thick solid, dashed, and dotted lines are for σ = 10, 1, and 0.9 respectively. The first two curves have Hill coefficients of 2 and 1. Calculations for σ > 10 are indistinguishable from the solid line. For comparison, the thin solid line is for nonamplified specificity: formula image (B) Steady-state W* as function of K2, the dissociation constant between phosphatase E2 and its protein substrate W*. K1 is kept at 0.01. The thick solid, dashed, and dotted lines are for σ = 0.1, 1, and 1.1, respectively. Calculations for σ < 0.1 are indistinguishable from the solid line. Again, the thin solid line is for nonamplified specificity with Hill coefficient 1: formula image
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Comment on

References

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