Purification and comparison of enzymatic properties of endogenous transglutaminase between silver carp and black carp

Objective: This study aimed to investigate the differences in enzymatic properties of endogenous transglutaminase （TGase） in silver carp and black carp. Methods: STG and BTG were purified from the muscle of silver carp and black carp, respectively, by 80% ammonium sulfate precipitation, Q-Sepharose FF, and Sephacryl S-200 HR chromatographies. Two enzymes were analyzed for relative molecular weights, peptide sequences, secondary structures, optimal reaction conditions, and thermal inactivation kinetics. Results: The purified STG and BTG showed similar relative molecular weights, of which the enzyme activities were 14.34 U/mg and 12.67 U/mg, respectively. Both enzymes showed differences in peptide sequences. The secondary structures of them were mainly the β-fold, though the content of β-fold in STG was slightly higher than that of BTG. The optimal temperatures for STG and BTG were both 50 ℃, and the optimal pH values were 8.0 and 7.5, respectively. The enzymes required Ca2+ up to 1 mmol/L for full activation. The activities of STG and BTG were enhanced by DTT, whereas PMSF, NH4Cl, NEM, EDTA, Cu2+, Ba2+, Zn2+, and Mg2+ showed inhibitory effects. When the temperature was 37~50 ℃, the passivations of STG and BTG by thermal treatment conformed to the first-order exponential decay kinetics with similar values of Ea. Conclusion: The primary and secondary structures of STG and BTG exhibited obvious differences, yet they still exhibited similar properties in terms of optimal reaction conditions and thermal inactivation kinetics.