Molecular cloning and tissue distribution of hyaluronan binding protein 2 (HABP2) in red sea bream Pagrus major

Quality improvement of threadfin bream (Nemipterus virgatus) surimi-gel using soy protein as a natural food additive

Previously, we identified sarcoplasmic serine proteinase (SSP) as a modori-inducing proteinase from threadfin bream belly muscle. In this study, we investigated the autolytic activity of commercial threadfin bream surimi under modori-inducing conditions. High autolytic activity was detected in commercial surimi and was inhibited by a soybean trypsin inhibitor, indicating that SSP still remained in the commercial surimi. The effects of soy protein, defatted soy protein (DSP) and isolated soy protein (ISP), on SSP activity and surimi-gel properties were evaluated. The results showed that the modori phenomenon was induced at 70 °C, and that both DSP and ISP suppressed SSP activity and strengthened the breaking strength and breaking distance of the modori-induced gel. Surimi-gel with DSP performed better on gel whiteness than that of ISP, and 1 g/kg DSP had optimal gel properties. In conclusion, soy protein proved to be a good natural food additive for surimi-gel production of threadfin bream.

Distinct enzyme activities of serine protease p37k in silkworm midgut and molting fluid

Serine proteases possess various biological functions. The serine protease p37k exhibits gelatinolytic activity in the silkworm midgut and degrades cuticular proteins in the molting fluid. In this study, we analyzed the activity changes of recombinant p37k (re-p37k) and p37k in the midgut and molting fluid of Bombyx mori. Firstly, in vitro-expressed re-p37k was activated when a 22 kDa band was observed by western blot. Re-p37k exhibits strong gelatinolytic activity, with the highest activity observed at pH 7.0-9.0 and 45 °C. Compared to p37k in the midgut, re-p37k loses thermal stability but can be restored by midgut extract or ions. E64, AEBSF, and an inhibitor cocktail inhibited the hydrolytic activity of re-p37k on epidermal proteins but did not inhibit the gelatinolytic activity. Subsequently, zymography showed that the positions of gelatinolytic band produced by p37k in the midgut and molting fluid were different, 35 kDa and 40 kDa, respectively. Finally, when heated midgut extract was added to re-p37k or molting fluid, the gelatinolytic band shifted from 40 kDa to 35 kDa, and the proteolytic activity of p37k in the molting fluid was inhibited. Collectively, our results demonstrate that p37k exhibits different activities in various tissues, suggesting its distinct tissue-specific functions during insect metamorphosis.

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.