Spectra broad multicolor high range protein ladder standard

A total of 0.02 g of gelatin sample was pretreated according to the method introduced by Zhang et al. (2020) [6 (link)]. Then, a volume of 10 μL of gelatin sample was loaded onto 10% SurePAGE Bis-Tris gels (GenScript, Nanjing, China). The applied electrophoresis voltage and electrophoresis time were 120 V and 80 min, respectively. The SpectraTM Broad Multicolor High Range Protein Ladder Standard (10–180 kDa, GenScript, Nanjing, China) was applied in this study as the protein standard. The electrophoresis gel was treated with a staining solution (1 g/L Coomassie Brilliant Blue R-250, 0.25 g/mL isopropanol and 0.1 g/mL acetic acid) for 2 h, and it was then treated with a destaining solution (0.2 g/mL ethanol and 0.1 g/mL acetic acid). When clear bands were observed, the gel was taken out and photographed with a digital camera.

Skins (tilapia, grass carp, and sea perch) were provided by Guangxi Luchi Agriculture Co., Ltd. (Nanning, China); fresh fish skins were frozen under −18 °C, and then transported to the laboratory in refrigerated trucks. The fish skin was manually stripped of scales and muscle fragments using a knife, thoroughly washed in tap water, frozen, and stored at −20 °C before use. Other materials used include trypsin (250 U/mg) (Shanghai Macklin Biochemical Technology Co., Ltd., Shanghai, China), 10% SurePAGE Bis-Tris gels (GenScript, Nanjing, China), and SpectraTM Broad Multicolor High Range Protein Ladder Standard (10–180 kDa, GenScript, Nanjing, China).