Originally Posted by
peptideguru
In freeze dried form, just the structure of the peptide. I'm not aware of any specific causes but it varies with all peptides, with no regards to size or structure.
It's completely different from how they react in the body too if that's how you mean? - MT1 for example has a half life of 1 hour, whereas MT2 has a half life of ~33 hours.
This is because the MT2 peptide is 'cyclic', which means it joins back up to itself, which results in less sites for enzymes to break the peptide down, whereas MT1 has many.