Abstract: This study aimed to investigate the enzyme that might be involved in this process. Cathepsin L was purified to homogeneity from the hepatopancreas of Litopenaeus vannamei, and its molecular mass was approximately 31 kD as analyzed by sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE). Peptide mass fingerprinting revealed that 8 peptide fragments with a total of 112 amino acid residues were completely identical to the cathepsin L gene of L. vannamei. Using Z-Phe-Arg-MCA as substrate, the proteinase revealed optimal activity at 35 ℃ and pH 5.5, respectively. Purified cathepsin L was stable at temperature up to 40 ℃ and in the pH range from 5.5 to 6.5. It exhibited high specificity towards the substrate Z-Phe-Arg-MCA. Its enzymatic activity was significantly suppressed by the cysteine proteinase inhibitors E-64 and leupeptin, while it could be slightly activated by the metalloproteinase inhibitors ethylene diamine tetraacetic acid (EDTA) and ethylene glycol tetraacetic acid (EGTA). In addition, the fibrous structure of shrimp meat was increasingly destroyed with the prolongation of cold storage time as observed by scanning electron microscope (SEM). Purified cathepsin L effectively hydrolyzed muscular proteins as detected by SDS-PAGE, suggesting its potential involvement in the degradation of shrimp muscular proteins during cold storage.

Key words: Litopenaeus vannamei, cathepsin L, purification, myofibillar protein, degradation, scanning electron microscope (SEM)