Transglutaminases (EC 2.3.2.13) are a group of thiol enzymes that catalyse acyl-transfer reaction in which the gamma-carboxyamide groups of peptide-bound glutaminyl residues are the acyl donors. They cause post-translational modification of proteins mainly by protein to protein cross-linking, but also through acyl transfer reaction and deamidation of glutamine residues. / Crude liver and flesh extracts of bluefish (Pomatomus saltatrix ) were investigated to ascertain the effects of storage time and temperature on the stability and activity of transglutaminase (TGase). TGase activity was measured and the enzyme was subsequently characterized using CBZ-L-glutaminylglycine and hydroxylamine as substrates. Frozen bluefish liver and flesh extracts had higher specific activities (0.321 Units and 0.230 Units respectively) in comparison to refrigerated liver and flesh extracts (0.124 Units and 0.071 Units respectively) at the end of a 30 day storage period with the frozen liver extract retaining the highest stability. The optimum temperature for the crude bluefish liver TGase reaction with CBZ-L-glutaminylglycine and hydroxylamine was between 40°C and 45°C. The enzyme was stable at temperatures below 55°C, beyond which it lost activity progressively. The crude enzyme extract was active within the pH range of 6.0-7.5, with an optimum pH of 7.0, and was stable from pH 6.5-8.0. / TGase was partially purified from the frozen liver extract of bluefish by gel filtration on 8ephacryl S-200 HR. The partially purified extract was further characterized with respect to its response to temperature and pH. The effects of sodium as well as calcium chloride and other divalent cations, and the inhibitory effects of various chemicals on the activity of the partially purified TGase were also investigated. The partially purified bluefish TGase had an optimum temperature of 40°C via the reaction with CBZ-L-glutaminylglycine and hydroxylamine. The enzyme was observed to be stable at temperatures below 50°C and approximately 90% of the initial TGase activity was retained at the end of a 30 min incubation period. The partially purified bluefish TGase had a pH optimum of pH 7.5 and was stable within a narrow pH range of 7.0 - 8.0. / The partially purified enzyme showed requirement for calcium (Ca 2+) ions for activity and no activity was observed in the absence of Ca2+. The replacement of Ca2+ by other divalent cations such as Mg2+, Mn2+, Ba2+, Zn2+ and Fe2+ produced various levels of activity with the enzyme, albeit less than that achieved with Ca2+. Increasing NaCl concentrations, 0 - 15mM, did not seem to have an enhancing effect on the activity of partially purified bluefish TGase. TGase was inhibited by sulfhydryl alkylating agents (monoiodoacetic acid (IAA) and N'-ethylmaleimide (NEM)).

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