How to distinguish a cyclic peptide from a linear peptide?

Question

How to distinguish a cyclic peptide from a linear peptide?

Answer 1

Maybe you could test for sensitivity to aminopeptidase and carboxypeptidase? A linear peptide would presumably be degraded by either, while a cyclic one may be resistant.

Depending on the amino acid sequence, you could also test for presence/absence of a free amino terminus, based on whether the peptide could be modified with an amine-specific reporter (like fluorescein isothiocyanate, for example).

Answer 2

hmm thats a hard one

Answer 3

Tricky...

I like quetzal's suggestions.

You could also possibly determine the pI of the peptide. Normally, the C and N termini contribute substantially to the pI - but a cyclic peptide has no c or n termini, so its pI would derive solely from the amino acid side-chains...

Sensitive enough mass spec might also be able to detect the difference.

And its HPLC profile would change slightly, as it would be more hydrophobic...

Answer 4

Difference will be observed in hydrodynamic properties, like sedimentation coefficient etc.