SDS-PAGE analysis of expression of human collagen II in P. pastoris shake flask cultivation (experiment 3, Table 1 ) after 21, 46 and 72 hours cultivation Figure 4 SDS-PAGE analysis of expression of human collagen II in P. pastoris shake flask cultivation (experiment 3, Table 1 ) after 21, 46 and 72 hours cultivation. R represents a reference culture with pulse feeding of methanol and F predetermined quasi-continuous feed. Collagen chains were derived from correctly folded collagen II molecules by HCl-extraction and pepsin digestion. The collagen II chains are marked with an arrow.