If you take collagen and treat it with a reagent that has two different crosslinkers in the sme molecule, ie one with a maleimide group on one end and a succinamide ester on the other end, you can get the amines on the collagen to react with the succinamide esters. Then if you take thiopyrophosphate, you can add this to the labelled collagen by getting the thiol group to react with the maleimide esters that are now part of the labelled collagen.

You can reach me at [email protected] for ways to do this or for more details, or just ask for them here and I will try to answer any questions you may have.

This is of course one way to do things.