Glucose-6-phosphate Isomerase Is an Endogenous Inhibitor to Myofibril-Bound Serine Proteinase of Crucian Carp (Carassius auratus)

Abstract

Glucose-6-phosphate isomerase (GPI) was purified to homogeneity from the skeletal muscle of crucian carp ( Carassius auratus ) by ammonium sulfate fractionation, column chromatographies of Q-Sepharose, SP-Sepharose, and Superdex 200 with a yield of 8.0%, and purification folds of 468. The molecular mass of GPI was 120 kDa as estimated by gel filtration, while on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two subunits (55 and 65 kDa) were identified, suggesting that it is a heterodimer. Interestingly, GPI revealed specific inhibitory activity toward a myofibril-bound serine proteinase (MBSP) from crucian carp, while no inhibitory activity was identified toward other serine proteinases, such as white croaker MBSP and crucian carp trypsin. Kinetic analysis showed that GPI is a competitive inhibitor toward MBSP, and the K(i) was 0.32 microM. Our present results indicated that the multifunctional protein GPI is an endogenous inhibitor to MBSP and may play a significant role in the regulation of muscular protein metabolism in vivo.

Mung Bean Trypsin Inhibitor Is Effective in Suppressing the Degradation of Myofibrillar Proteins in the Skeletal Muscle of Blue Scad (Decapterus maruadsi)

“…Endogenous proteinase inhibitors are important tools for regulating the proteolytic activity of their target proteinases by suppressing these in emergency cases or for signaling receptor interactions or clearance . Our previous studies have indicated that endogenous inhibitors to MBSP are actually glucose-6-phosphate isomerases with molecular masses of approximately 55 kDa in monomer form and 110 kDa in dimer form . However, the application of glucose-6-phosphate isomerase in fish surimi production is still inappropriate because isolation of this protein from the sarcoplasmic fraction is cost-consuming and loses activity quickly at the temperature above 55 °C.…”

“…Our previous studies have indicated that endogenous inhibitors to MBSP are actually glucose-6-phosphate isomerases with molecular masses of approximately 55 kDa in monomer form (12) and 110 kDa in dimer form (13). However, the application of glucose-6-phosphate isomerase in fish surimi production is still inappropriate because isolation of this protein from the sarcoplasmic fraction is cost-consuming and loses activity quickly at the temperature above 55 °C.…”

“…MBSPs have been purified from not only freshwater fish common carp and crucian carp but also marine lizard fish . Its endogenous myofibril-bound serine proteinase inhibitor (MBSPI), which was actually glucose-6-phosphate isomerase, has also been elucidated , . On the basis of previous research results, we proposed that MBSP is most likely the enzyme that is responsible for the modori phenomenon in fish, although the possibility of the involvement of cathepsin (cathepsins B and L) should not be excluded.…”

Engineered Proteolytic Nanobodies Reduce Aβ Burden and Ameliorate Aβ-Induced Cytotoxicity

“…A BLAST sequence search using the eight amino acid sequence stretch encompassing the R-secretase site of Aβ (HHQKLVFF) identified phosphoglucose isomerase (PGI) as the top hit. PGI, a 120 kDa protein made up of two subunits (55 and 65 kDa) (27), contains a Lys-Leu sequence homologous to the R-secretase site of Aβ along with several other lysine and arginine residues which represent potential cleavage sites for serine proteases. Hence, we selected PGI as a control protein to test for off-target proteolytic activity of Asec-1A.…”

Identification by GeLC‐MS/MS of Trypsin Inhibitor in Sarcoplasmic Proteins of Three Tropical Fish and Characterization of Their Inhibitory Properties

“…Therefore, sarcoplasmic protein might be an alternative ingredient for controlling proteolysis of proteinase‐laden muscle proteins. Endogenous muscular proteinase inhibitors have been reported in freshwater fish including common carp and crucian carp (Sun and others ; Siriangkanakun and Yongsawatdigul ). However, there is limited information on endogenous proteinase inhibitors in marine fish species that are economically important to seafood industry, particularly threadfin bream ( Nemipterus spp.…”