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Sci. Signal., 3 January 2012
Vol. 5, Issue 205, p. lc2
[DOI: 10.1126/scisignal.2002716]

LETTERS

Response to Comment on "‘Load-Induced Modulation of Signal Transduction Networks’: Reconciling Ultrasensitivity with Bifunctionality?"

Peng Jiang1, Alejandra C. Ventura2, Eduardo D. Sontag3, Sofia D. Merajver4, Alexander J. Ninfa1*, and Domitilla Del Vecchio5*

1 Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109–0606, USA.
2 Instituto de Fisiología, Biología Molecular y Neurosciencias, COINCET-UBA, and Laboratorio de Fisiología y Biología Molecular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA, Argentina.
3 Department of Mathematics, Rutgers University, New Brunswick, NJ 08854–8019, USA.
4 Department of Internal Medicine, Comprehensive Cancer Center, University of Michigan, Ann Arbor, MI 48109, USA.
5 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Abstract: Straube suggests that a model that reflects the bifunctional nature of the cycle enzyme uridylyltransferase/uridylyl-removing enzyme (UTase/UR) should be used, in which the UT and UR activities are distinct and reciprocally regulated activity states of the enzyme, and notes that if such a model is used, the effects of retroactivity at intermediate stimulation will be different. However, such a model does not accurately match the observed enzyme regulatory properties and fails to predict the ultrasensitive response obtained in the experiments. Here, we argue that modeling the UTase/UR enzyme as a bifunctional enzyme with reciprocally regulated activity states misses important aspects of the system.

* Corresponding authors. E-mail, aninfa{at}umich.edu (A.J.N.); ddv{at}mit.edu (D.D.V.)

Citation: P. Jiang, A. C. Ventura, E. D. Sontag, S. D. Merajver, A. J. Ninfa, D. Del Vecchio, Response to Comment on "‘Load-Induced Modulation of Signal Transduction Networks’: Reconciling Ultrasensitivity with Bifunctionality?". Sci. Signal. 5, lc2 (2012).

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