Biochemical Properties of Collagen from Four Flatfish Species in Cold Area: In Relation to Physiological Temperature and Amino Acid Composition

Collagen (ASC) was purified from four flatfish species (Greenland halibut, blackfin flounder, stone flounder, and slime flounder) collected from a cold area in Japan to investigate their biochemical properties. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis pattern, Fourier transform infrared spectroscopy, and circular dichroism analysis revealed the typical structure of type I collagen. The denaturation temperature (Td) of ASC positively correlated with the physiological temperature (Tp) using previously reported data, which were obtained from fish (a total of 32 species). In this study, the lowest hydroxyproline (Hyp)/Pro/imino acid (Pro + Hyp) content was observed in Greenland halibut ASC (Tp is lowest), whereas the highest Ser content was observed in slime flounder ASC (Tp is highest). Using the data obtained from a previous study, a positive/negative correlation could be found between Td and Hyp/Ser, which is consistent with our previous reports. The Pro content in the present data followed the pattern of Hyp but exceeded the value predicted from Td by approximately 30 residues. These results may suggest that the collagen extracted from four flatfish in the cold area adopted decreasing imino acid content and increasing serine content for their adaptation.