I'm having trouble dissolving collagen that has been obtained by enzymatic hydrolysis, using a phosphate buffer as a medium for the hydrolysis. Once the collagen has been dialyzed and lyophilized I need to dissolve it in acetic acid ( 0.1 mol/L) to measure the denaturation temperature, but nothing seems to happen. Does anyone have an idea of what could be happening? Is there a possible phosphate-collagen complex that's preventing the collagen to solubilize?