Purification and characterization of a sarcoplasmic serine proteinase from threadfin bream Nemipterus virgatus muscle

A sarcoplasmic serine proteinase (SSP) was purified from threadfin bream (Nemipterus virgatus) belly muscle by ammonium sulfate precipitation and a series of chromatographies including Q-Sepharose, Phenyl Sepharose and Superdex 200. The SSP was purified 1967 folds with a yield of 4.8%. The molecular weight of the SSP was estimated to be 43.5 kDa and 22.5 kDa on SDS-PAGE under non-reducing and reducing conditions, respectively. The N-terminal amino acid sequence of the two protein bands were determined as IVGGYEXQPYSQAHQVSLNSGY and corresponded. It is suggested that the SSP exists as a homodimer. Optimum pH and temperature were 9.5 and 50 °C, using Boc-Val-Pro-Arg-MCA as a substrate. Substrate specificity and effects of inhibitors indicated that the SSP was a trypsin-like serine proteinase. The SSP was responsible for hydrolyzing myosin heavy chain (MHC) and inducing modori phenomenon in the threadfin bream surimi gel. Thus, the SSP was considered as a modori-inducing proteinase.