Study Of Glucose-6-phosphate Isomerase From Sliver Carp And Blue Scad Skeletal Muscle

Modori phenomenon often occurs during the manufacturing process of surimi, affecting thequality of surimi products eventually. Researches have showed that modori effect was caused byendogenous proteinase, such as cathepsin B、L and myofibril-bound serine proteinase (MBSP).MBSP might be the major reason of the modori phenomenon. In order to produce high-qualitysurimi products, the efficient MBSPI are demanding in protecting myofibrillar proteins fromproteolysis by MBSP. In the present study, GPIs which could inhibit the activity of MBSP, wrepurified from the skeletal muscle of sliver carp (Hypophthalmichthys molitrix) and blue scad(Decapterus maruadsi), and we studyed the characters of the GPI. This will be a theory aboutimproving the quality of surimi products and using fish proteins effectively.Two GPIs were purified by ammonium sulfate fractionation, column chromatographies ofQ-Sepharose and SP-Sepharose from sliver carp and blue scad. The results showed that, the yieldof sliver carp GPI and blue scad GPI was6.6%and6.9%, and the purification fold was21.8and199.9respectively. Western blot analysis revealed positive reaction bands using rat againstwhite croaker MBSPI (GPI) polyclonal antibody.The optimal pH and optimal temperature of silver carp GPI was8.5and50℃; the optimalpH and optimal temperature of blue scad GPI was8.0and40℃, respectively. Eleven highersignal-noise ratio peptide fragments of the enzyme from silver carp were subjected toMALDI-TOF/TOF-MS/MS analysis, all the eleven peptide fragments revealed100%identity tophosphoglucose isomerase-2from zebrafish (Danio rerio), suggesting the purified enzyme fromsilver carp was GPI.GPI from silver carp revealed specific inhibitory activity toward myofibril-bound serineproteinase (MBSP) from crucian carp, while no inhibitory activity was identified toward pigtrypsin, pig chymotrypsin, snakehead trypsin, pacific white shrimp trypsin, mantis shrimp trypsin,silver carp trypsin and silver carp chymotrypsin. With the increasing of the concentration aboutblue scad GPI, the degradation of myofibrillar proteins was inhibited.When the addition of silver carp GPI reached0.031%of the minced fish meat, a9.2%increase of gel strength was dectected, while the addition of blue scad GPI reached0.024%,modori phenomenon occurred in the surimi products. These results strongly suggested that the endogenous MBSP inhibitor was effective and species-dependent.