SDS-polyacrylamide gel electrophoresis (SDS-PAGE)
Electrophoretic patterns of different species of collagens were analysed according to the method [19]. The samples
were dissolved in 50 g/L SDS solution. The mixtures were then heated at 850C for 1 h, followed by centrifugation at
8500g for 5 min to remove undissolved debris. Solubilized samples were mixed with the sample buffer (0.5 mol/L
Tris–HCl, pH 6.8 containing 40 g/L SDS, 200 mL/L glycerol in the presence or absence of 100 mL/L
βmercaptoethanol) with the ratio of 1:1 (volume ratio). The mixtures were loaded onto a polyacrylamide gel made of
75 g/L separating gel and 40 g/L stacking gel and subjected to electrophoresis at a constant current of 20 mA/gel.
After electrophoresis, gels were fixed with a mixture of 500 mL/L methanol and 100 mL/L acetic acid for 30 min,
followed by staining with 0.5 mL/L Coomassie blue R-250 in 150 mL/L methanol and 50 mL/L acetic acid for 1 h.
Finally, they were destained with a mixture of 300 mL/L methanol and 100 mL/L acetic acid for 1 h and destained
again with the same solution for 30 min. High molecular weight protein markers were used to estimate the molecular
weight of proteins. Type I collagen from calf skin was used as standard collagens.