Biochemical and physiological properties of the enzyme responsible for formaldehyde formation in fish during storage

Supervisors: Vibeke Barkholt (DTU) and Bo M. Jørgensen (DIFRES)

The enzyme trimethylamine-n-oxide aldolase (EC 4.1.2.32) is a lyase, catalysing the splitting of TMAO to dimethylamine (DMA) and formaldehyde. The enzyme activity is found in gadoid fish, in high amount in kidney and spleen, and in gall bladder and gall juice. Some activity is found in muscle, of that most in the red muscle type. Although the activity in fillets is low, it becomes important during long-time storage. In particular, this applies to fish stored frozen at a relatively high temperature (e.g. -18°C) and to dried fish, because the enzyme is concentrated in the unfrozen or remaining water fraction, respectively. The physiological relevance of the enzyme is unknown. Splitting of TMAO is probably not its in vivo function But it has been shown that its activity is fully responsible for development of formaldehyde during frozen storage of a variety of fish species. The project aim at identifying if the enzyme has actually another, physiologically relevant, activity.

For that purpose the following project elements will be conducted:

• Improving the enzyme preparation.
• Molecular characterisation of the enzyme: Size, subunit composition, amino acid sequence.
• Comparison of the amino acid sequence with known sequences found in databases accessible via the internet.
• Raising of antibodies against the enzyme.