Pyridinoline concentrations in muscular and skin collagen of fish and relationship between collagen solubility and pyridinoline concentration in fish muscular collagen

Pyridinoline (Pyr), one of the mature crosslinks of collagen, was determined in muscular collagen of three species of fish. The amounts of muscular Pyr in red sea bream, yellowtail, and tiger puffer were 3.4, 8.8, and 50.3 mmol/mol collagen, respectively, indicating that the Pyr concentration in muscular collagen differs greatly among fish species. The Pyr concentration in tiger puffer muscular collagen was the greatest, but it was only one-fourth that in rabbit muscle. As in mammalian skin collagen, Pyr was not detected in skin collagen of red sea bream and yellowtail. However, tiger puffer skin contained Pyr (3.75 mmol/mol collagen). The presence of Pyr would have a relationship to some features of tiger puffer skin, such as mechanical strength and thickness. Pyr concentrations in acid-soluble collagen (ASC), pepsin-solubilized collagen (PSC), and insoluble collagen (ISC) in muscles of three species of fish were determined. Pyr was found in ISC > PSC > ASC, from the highest to the lowest concentration, and the concentration in ISC was 45–200 times that in ASC. Therefore, Pyr crosslinks that are formed between collagen molecules would have a close relationship to collagen solubility.