Response to comment on "'load-induced modulation of signal transduction networks': reconciling ultrasensitivity with bifunctionality?".

1Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109-0606, USA.
Science Signaling (Impact Factor: 7.65). 01/2012; 5(205):lc2. DOI: 10.1126/scisignal.2002716
Source: PubMed

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.