Migration of circular DNA vs circular/crosslinked peptide in gels - (Aug/11/2015 )

As I understand it:

1. Relaxed circular DNA migrates slower on a gel than linearized DNA (e.g. here)

2. Circular peptides (or intra-crosslinked peptides) run faster on a gel than linearized peptide

--> So circular DNA runs slower and circular peptides run faster than their linear counterparts.

Why the difference? 

I do not see any relationship between DNA and peptides from your condition, how did you get such conclusion?

Circular, or internally crosslinked peptides run faster on an acrylamide (sieving) gel than its linearized counterpart. I have seen this many times and is pretty common knowledge. This makes sense because circular (e.g. disulfide intra-chain crosslinked) peptides are more compact than their linear (e.g. fully reduced) counterparts, and thus travel through the acrylamide matrix faster.

On the other hand, relaxed circular (e.g. nicked non-supercoiled) DNA travels slower than than its linearized (e.g. digested) counterpart in an agarose (sieving) gel. For example, see this gel. 

Same principles, same concept, yet two different migration patterns.