QUESTIONS: alpha-helix "signals" in proteins

murphy kenneth p kpmurphy at
Fri Jul 8 09:38:02 EST 1994

In article <2vj0dsINN2qfk at>,
Richard Engh <engh at> wrote:
>Sorry if this point has become peripheral, but regarding thermodynamic
>vs. kinetic control, I think the serpins are relevant:
>murphy kenneth p (kpmurphy at wrote:
>: But isn't there a cleavage involved in obtaining the "latent" state?  This 
>:really difines a new system and it's entirely possible that the global minimum
>: is differen in this new system.  I really don't see the serpin example as 
>: directly addressing the issue of thermodynamic vs kinetic "control".
>The serpin plasminogen activator inhibitor-1 becomes latent WITHOUT any
>cleavage.  The latent structure is similar to other cleaved serpin structures,
>except that is it not cleaved.  Prior to the conversion to latency, it is
>in a conformation which is different, possibly flexible or mobile, which is
>an inhibitory form.  The only factors which influence the global minimum
>in vivo will be complexation with ligands (e.g. vitronectin) or other environ-
>mental factors.  The protein in vitro shows kinetic control in that there
>is a significant lifetime for the inhibitory state, before the irreversible
>final folding to a more global minimum latent state.  I don't know what the
>current opinion is regarding the in vivo situation, where further factors
>will influence both kinetics and thermodynamics.

Thanks for the information.  I wasn't aware that there was no cleavage in this


Dr. Kenneth P. Murphy				e-mail: k-murphy at
Department of Biochemistry			office: (319)335-8910
Univeristy of Iowa				lab:  (319)335-7936
Iowa City, IA 52242            		        FAX:  (319)335-9570

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