For characterization of collagen, SDS-PAGE is usually carried out with reducing (in presence of beta mercaptoethanol) and non-reducing conditions. In all the published article I found, all collagen under both of the conditions showed similar bands and authors concluded that there is no disulfide bond and the collagen is type I collagen. I extracted collagen from a fish bone and found different bands in reducing and non-reducing conditions, I mean one extra lower molecular weight band under reducing condition. How can I describe my result? It is noted that my extracted collagen contains 4 Cysteine/1000 residues.
Raju: As you had mentioned that type I collagen contains no disulfide bond thus shown no difference in migration pattern under either reducing or non-reducing SDS-PAGE. As there are more than 20 different collagen types in different tissues with various functions, the presence and number of S-S bond(s) results in different migration patterns in the two electrophoretic conditions. You can identify the location of these 4/1000 cysteines and how the (at least) one or two disulfide bond is formed (between 1-2, 1-3, 1-4, 2-3, 2-4, or 3-4) thus explaining the secondary structure of your new collagen which may help to determine its tertiary structure and function(s). Good luck.
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