cis-trans Pro and better substrates

[tivol at tethys.ph.albany.edu]

In article <9411291932.AA16099 at spartan.ac.BrockU.CA>,
jatkin at SPARTAN.AC.BROCKU.CA writes:
>        How then can we speak of either the cis or the trans-Pro conformer
>as being a preferred substrate?  It is the peptide that is the substrate. 
>One may only suppose that one solution form reacts preferentially to
>another. 
> 
If the transition from cis to trans (& trans->cis) is slow compared to binding,
cleavage, etc., then it makes sense to treat the cis form and the trans form
as different substrates--you would certainly treat a peptide containing a d-
amino acid and an l-a.a. as different even though there is a finite rate for
rascimization (sp?).

>        Can anyone comment on the ease with which the equilibrium is
>established for small peptides?

Clearly the key point.  If equilibrium is established only slowly, then adding
only one conformer to the reaction mix gives a situation which is not at equi-
librium (as is the case with many biochemical reactions).
				Yours,
				Bill Tivol