What one can learn from experiments about the elusive transition state?
  We present the results of an exact analysis of a model energy landscape of a protein to clarify the notion of the transition state and the physical meaning of the $\phi$ values determined in protein engineering experiments. We benchmark our findings to various theoretical approaches proposed in the literature for the identification and characterization of the transition state. 
Iksoo Chang, Marek Cieplak, Jayanth R. Banavar, and Amos Maritan