H-bonding side-chains

[colby]

Baron0805 wrote:
> 
> I looked in my Cell book to see what you were talking about.  Both of these
> structures are very stable structures.  Tryptphan is stabilized by the ring
> structures and Arginine is stabilized by its resonance ability.  I would say
> that these two amino acids are able to H-bond, but it is very unlikely due to
> resonance.  That would be my guess.

Thanks for your reply. It prompts me to ask why histidine is able to
accept a H-bond - in fact both N-atoms in the His sidechain can be
H-bond acceptors. Does histidine not have resonance stabilization too?
(You can find details at
http://swift.embl-heidelberg.de/future/aainfo/hbonds.html).

-colby