Abstract
To elucidate the roles of 5'-nucleotidase in freshness lowering of fish muscle, the effects of some muscle constituents and various substances on the activities of membrane-bound and cytosol 5'-nucleotidase isolated from the white muscle of black rockfish Sebastes inermis were examined. And the activities of both enzymes, nucleotide composition and the K-value of black rockfish white muscle were estimated during postmortem storage at 4°C, simultaneously.
Both enzymes were inhibited strongly by ADP and ATP, and activated by a high concentration (5-10mM) of phosphocreatine. In the muscle of black rockfish, 5'-nucleotidase activity was observed to decrease from the initial value to a minimum at 1-2 days of storage, then to increase gradually to a maximum after 4 days keeping pace with the decrease of phosphocreatine and the rise and fall of ADP. This change in enzyme activity may be assumed to be influenced by the concentrations of these metabolites, and may result in the changes in IMP content and the freshness of fish, viz. the K-value.
