Hydroxylysyl-pyridinoline occurrence and chemical characteristics of collagen present in jumbo squid (Dosidicus gigas) tissues

Hydroxylysyl-pyridinoline (HP) occurrence and chemical characteristics of collagen from jumbo squid tissues were investigated. Muscle collagen (MC) was higher in Glu, Arg and Gly, but lower in hydrophobic amino acids compared with skin collagen (SC). Lys hydroxylation (%) was higher (P < 0.05) in MC (46.9 ± 4.01) than SC (23.4 ± 1.70). Carbohydrate content (% dry wt.) was similar (P ≥ 0.05) among MC (16.6 ± 0.53) and SC (15.2 ± 1.12), showing arabinose (MC, 11.1 ± 0.21 vs. SC, 11.7 ± 0.91), glucose (MC, 3.3 ± 0.10 vs. SC, 2.8 ± 0.10, P < 0.05) and xylose (MC, 0.9 ± 0.10 vs. SC, 0.7 ± 0.11, P < 0.05); mannose (1.1 ± 0.11) and galactose (0.2 ± 0.01) were found only in MC. FT-IR analysis suggests major supra-organizational rearrangement in MC than SC, through presence of more stable triple-helix structures associated to Gly, Hyl, polar amino acids and carbohydrate contents. HP chemical nature and its tissue-specific distribution (MC, 4.6 mmol/mol collagen) indicate that specific Lys hydroxylation can be a critical regulatory step on cross-link formation. Chemical composition variations and HP distribution suggest squid collagens have quite different biomechanical requirements, i.e., muscle or skin collagen rigidity or elasticity.