The existence of aspolin and its trimethylamine‐N‐oxide demethylating activity in the muscle of freshwater fish

• Published in: Fisheries science Vol. 71; no. 4; pp. 904 - 913
• Main Authors: KIMURA, Meiko, TAKEUCHI, Kazuharu, KIMURA, Ikuo, SEKI, Nobuo
• Format: Journal Article
• Language: English
• Published: Melbourne, Australia Blackwell Science Pty 01.08.2005; Springer Nature B.V
• Subjects: Amino acids; aspolin; Carp; Cyprinus carpio; Electrophoresis; Enzymatic activity; Freshwater; Freshwater fish; polyaspartic acid; Polymers; Proteins; Residues; Theragra chalcogramma; trimethylamine‐N‐oxide; trimethylamine‐N‐oxide demethylase; walleye pollack
• ISSN: 0919-9268; 1444-2906
• DOI: 10.1111/j.1444-2906.2005.01044.x

Aspolin is a polyaspartic acid‐like protein, which is originally isolated from walleye pollack Theragra chalcogramma muscle as trimethylamine‐N‐oxide (TMAO) demethylase. Although carp Cyprinus carpio muscle contains a trace amount of the enzyme substrate, TMAO, aspolin can be extracted and purified by acid treatment, successive chromatographies and polyacrylamide gel electrophoresis, and has twice the amount of that in walleye pollack muscle. Carp aspolin showed a low enzymatic activity in the presence of Fe2+ and reductants, and its Km value (100 mM) to TMAO was extremely high. It was a thermostable protein and had an unfolded conformation. The amino acid sequence of carp aspolin 1 deduced from cDNA revealed that it contained a long Asp polymer, an uninterrupted stretch of 138 Asp residues, followed by four amino acid residues, His‐Glu‐Glu‐Leu, in C‐terminus. The chain length was shorter by 42 Asp residues than that of its walleye pollack counterpart.