4.9. Measurement of the Melting Temperature of Collagen

The collagen samples purified from the culture media of ZF4 cells by pepsin digestion and salt precipitation were dissolved in 10 mM acetic acid, and CD signals at 221 nm were measured with the J-820 CD spectropolarimeter (Jasco, Tokyo, Japan) equipped with a Peltier thermal controller while heating (0.25 °C/min). CD signals at 221 nm were normalized to the fraction folded. Tm values are temperatures at which fraction folded is 0.5.