Endogenous proteolytic enzymes in skeletal muscle: their significance in muscle physiology and during postmortem aging events in carcasses

Unlocking the secrets of crude myofibril-bound serine protease from grass carp: The role in degrading myofibrillar proteins

Grass carp (Ctenopharyngodon idella) are used as raw material for conventional surimi products in Southern China. However, endogenous serine proteases deteriorated the texture of the surimi gel. To unlock the mechanism behind, the present study isolated the crude myofibril-bound serine protease (cMBSP) in grass carp and studied its effects on surimi gel. The cMBSP activity was the highest at 40 °C and pH 8.0, and it remained stable at 20-55 °C neutral pH. Additionally, it was susceptible to serine protease inhibitors and high concentrations of Na+. The maximum degradation of myosin heavy chain by cMBSP was observed at 50 °C. Protein unc-45 homolog B (a myosin chaperone) is one of the apparent degradation products according to mass spectrometry. The cMBSP caused lower water holding capacity and deteriorated texture in the surimi gel. This study expanded insights about the mechanism of surimi gel degradation by cMBSP, which provided theoretical basis for enhancing surimi quality.

A novel function by cathepsin D in degradation of nucleic acids

Cathepsin D (CTSD) is an aspartic endopeptidase, however, we found that it was also capable of enzymatic digestion of nucleic acids (NAs). The purpose of this study was to investigate the basic properties of CTSD enzymatic activity on NAs, and explore the degradation mechanism. The results showed that NAs were efficiently digested between pH 3.0 and 5.0, and the optimum pH was 3.5. CTSD exhibited optimum activity at the temperature of 50°C. The degradation rate was improved with an increased CTSD concentration, and NAs were digested to an enzyme concentration of 0.001%, at which point, NAs were no longer digested. Ca2+ and Mg2+ at low concentrations of 5 mM promoted the digestion remarkably. As the protein substrate for CTSD, both Hb and BSA had no effect on DNA degradation, even when the molar ratio of protein:DNA was 104:1. Kinetic parameters of Km and kcat/Km value were (42 ± 1) μM and (1.62 ± 0.1) × 10-2 s-1mM-1 respectively, using real-time quantitative PCR (RT-PCR). Specially, pepstatin A which is the specific aspartic protease inhibitor exhibited inhibitory effect on NA digestion by CTSD as well, suggesting that the catalytic active site of CTSD for NAs might be the same as protein. A brief degradation mechanism is discussed. The present study may change the cognition of CTSD specificity for substrate and contribute greatly to enzymology of CTSD.

Effect of freezing on the quality of breast meat from broilers affected by wooden breast myopathy

The objective of the present study was to characterize possible variations in the quality of wooden chicken breast meat during freezing for 12 mo, in order to prove whether the shelf life recommended by the industry allows the storage of that type of meat without compromising its consumption. Three hundred samples of male Cobb 500 broilers slaughtered at 42 d of age were used. Part of the samples (n = 20 normal-control group; n = 20 moderate degree; n = 20 severe degree) were analyzed on the day of collection (beginning), previously kept under refrigeration (4°C). The other samples were stored (-18°C) for up to 12 mo. At the end of each proposed freezing period (3, 6, 9, and 12 mo), physical and chemical analyses were performed (per period: n = 20 normal-control group; n = 20 moderate degree; n = 20 severe degree). Color (L*, a*, and b*), pH, water-holding capacity, cooking losses, tenderness, lipid oxidation, chemical composition, cholesterol concentration, mineral profile, and collagen concentration were evaluated. The physicochemical quality of wooden chicken breast meat is significantly altered during frozen storage for 12 mo, being of inferior quality when compared to normal chicken breast meat, which can negatively affect consumer acceptance. However, it should be noted that even after 12 mo of freezing, the meats did not show oxidative rancidity.

Efficacy of multi-stage sous-vide cooking on tenderness of low value beef muscles

The efficacy of thermal activation of residual proteolytic enzymes on shear force and deformation of 72 beef supraspinatus (SS) and rectus femoris (RF) muscles was tested using multi-stage sous-vide cooking (M-SV; 1 h at 39 °C, 1 h at 49 °C, 4 h at 59 °C), single-stage sous-vide cooking (S-SV; 4 h at 59 °C), and waterbath cooking (22 min at 70 °C, to 59 °C). Two storage conditions (1 week at 2 °C; 2 weeks at -1.5 °C) followed, then meat was reheated to and tested at 55 °C. Shear force decreased by 17-21% with S-SV (P < 0.001) and appeared to affect both myofibrillar and collagen components, likely through heat activation of cathepsin B & L and 20S proteasome. A further 5-6% increase was realized with M-SV (P: SS = 0.006, RF = 0.12) affecting primarily the myofibrillar component, likely from calpain-2 activation. The degree of deformation increased with sous-vide cooking in general (P < 0.001). No meaningful effects of post-cooking storage were found (P > 0.05).

Partial protease activity characterization of squid (Todaropsis eblanae) mantle / Caracterización parcial de la actividad proteolítica del manto de pota (Todaropsis eblanae)

Proteolytic activity in mantle of Todaropsis eblanae was maximum at 40 and 65 °C. Several peaks of activity were detected over the pH range studied (1.5-9.5), indicating the presence of acidic, neutral and alkaline proteases, depending on the temperature. The substantial enzymic inhibition at acidic pH by the inhibitor trans-epoxysuccinyl-L-leucylamine-4-guanidine butane (E-64) revealed the pre dominance of lysosomal cysteine proteases (cathepsins) which showed higher activity at 65 °C than at 40 °C. At 65 °C and pH 5.5 metallo-proteases were also detected by the inhibition with phenanthroline. Serine protease activity predominated at neutral pH (higher at 40 °C than at 65 °C), and cysteine proteases were detected at alkaline pH. There was evidence of cathepsin B and L activity at 65 °C and to a lesser degree at 40 °C.

Biochemical traits of Ciauscolo, a spreadable typical Italian dry-cured sausage

Ciauscolo is a short-ripened fermented sausage manufactured in the Marche region (central Italy) that has recently received a protected geographical indication product classification (PGI). The aim of this study was the exploration of the biochemical traits of this traditional Italian salami, with a special focus on protein and lipid composition. Ciauscolo salami was characterized by pH of 5.1 and 0.91 water activity. A prevalence of lactic acid bacteria in the microbiota was found. The free amino acids and biogenic amines average content was 2657 and 255 mg/kg, respectively. With regards to lipids composition unsaturated fatty acids represented 63% and 72% of total and free fatty acids. Despite these results had wide statistical variability, attributable to differences in the processing parameters and raw matter used, some peculiar traits were found: (1) structural muscular proteins underwent to less proteolysis than sarcoplasmic ones; (2) glycogen phosphorylase, enolase, and aldolase were the most proteolyzed among the sacoplasmic proteins; (3) there was inverse correlation between histamine content and yeasts population, and a direct correlation between the gly-pro content and lactic acid bacteria counts; (4) the content of aspartic acid and methyonine seem to be a possible molecular marker able to distinguish between double and single milling.

Cathepsin D from the hepatopancreas of the cuttlefish (Sepia officinalis): purification and characterization

Cathepsin D from the hepatopancreas of cuttlefish ( Sepia officinalis ) was purified to homogeneity by precipitation with ammonium sulfate (30-60%, w/v), Sephadex G-100 gel filtration, Mono-S cation-exchange chromatography, Sephadex G-75 gel filtration, and Mono-S FPLC with a 54-fold increase in specific activity and 17% recovery. The molecular weight of the purified cathepsin D was estimated to be 37.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On the basis of the native-PAGE and hemoglobin zymography, the purified protease appeared as a single band. The optimum pH and temperature for the cathepsin D activity were pH 3.0 and 50 °C, respectively, using hemoglobin as a substrate. The purified enzyme was completely inhibited by pepstatin A; however, no inhibition was observed with phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid. Moreover, the activity was strongly inhibited by SDS and molybdate and enhanced by ATP. The purified cathepsin D was activated by Mg(2+), Ni(2+), Zn(2+), Cu(2+), Cd(2+), Sr(2+), and Co(2+) ions, whereas it was not affected by Na(+), K(+), and Ca(2+) ions. The N-terminal amino acid sequence of the first 13 amino acids of the purified cathepsin D was APTPEPLSNYMDA. S. officinalis cathepsin D, which showed high homology with cathepsin D from marine vertebrates and invertebrates, had a Pro residue at position 6 and a Ser residue at position 8, where Thr and Lys are common in all marine vertebrates cathepsins D. S. officinalis cathepsin D showed high efficiency for the hydrolysis of myofibrillar proteins extracted from cuttlefish muscle.

Preservation of the proteolytic activity of a bovine spleen lysosomal-enriched extract using various freezing conditions

The preservation of the proteolytic activity of a bovine spleen lysosomal-enriched (BSLE) extract was investigated. The BSLE extract (pH = 5.8), was subjected to storage under different conditions: refrigeration at 0 degrees C for 60 days; freezing at -20 degrees C -either directly or previously frozen in liquid nitrogen-, -80 degrees C and in liquid nitrogen; freeze-drying and stored at 0 degrees C; and freezing at -20 degrees C or in liquid nitrogen in the presence of glycerol and sorbitol as cryoprotectants. Freezing at low temperatures (-80 degrees C and in liquid nitrogen) was most effective for preserving about 100% of the initial activity of all cathepsins (B, B+L and D), as well as the activity of the extract on myofibrils, for two years. Freezing at -20 degrees C, on the contrary, led to significant (P < 0.01) losses of activity. Freeze-drying was able to preserve cathepsin activity, while it failed to maintain activity on myofibrils. Both cryoprotectants sorbitol and glycerol significantly (P < 0.01) enhanced enzyme preservation, particularly cathepsin D and the activity on myofibrils, even at a freezing temperature of -20 degrees C.

Purification and characterization of cathepsin L-like enzyme from the muscle of anchovy, Engraulis japonica

Results relative to inhibitory effects and substrate specificity indicated that a protease from the muscle of anchovy, Engraulis japonica, was a cathepsin L-like enzyme. The enzyme was activated by thiol reagents and inhibited by thiol-blocking reagents. The molecular weight was estimated to be 25.8 kDa by SDS-PAGE. The enzyme exhibited its maximal activity at pH 6.0 and 50 degrees C for casein and N-benzoyl-D, L-arginine-beta-naphthylamide. The enzyme hydrolyzed at the position of Phe1, Asn3, Val13, Glu14, Val19 and Gly24 of the insulin beta-chain. The K'm and kcat of the enzyme were 73.4 microM and 0.5 microM/min, respectively, toward Z-Phe-Arg-MNap.

Ultrasonication of lamb skeletal muscle fibres enhances postmortem proteolysis

The effect of ultrasound upon the postmortem proteolytic activity of muscle fibres was investigated. As a preliminary result it was demonstrated that ultrasonication released lysosomal enzymes from liver cells while cell membranes suffered little damage. Proteolysis brought about by endogenous proteinases after 2 days of fibre storage at 4 degrees C was assessed by means of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Ultrasonic treatment of fibres enhanced proteolytic activity, as shown by the increased intensity of 30-kDa region degradation bands. A distinct change featuring sonicated fibres was the degradation of an 87-kDa protein and the appearance of an 83-kDa peptide. Cell damage was not very extensive, although it depended upon ultrasonication and fibre conditions.

The role of ultimate pH in proteolysis and calpain/calpastatin activity in bovine muscle

Of a total of three Friesian cows, two of which had been treated with adrenalin before slaughter, Mm longissimus (LO), supraspinatus (SS), triceps brachii (TB) and rectus abdominis (RA) were sampled at different times post mortem (pm). pH, calpain/calpastatin activities and degradation of myofibrillar proteins, as evidenced by SDS-PAGE, were assessed. Contraction characteristics were measured by determining myofibrillar ATPase activities. Adrenalin treatment resulted in a high ultimate pH (6.48 +/- 0.40) and a faster decline pm of calpain I activity. The effect was similar in all four investigated muscles (72.4 +/- 5.4% decline at 24 h pm). The decline in calpain I activity in the control muscles was muscle-dependent and ranged from 22.8-74.3% at 24 h pm. Differences in ultimate pH did not lead to distinct rates of breakdown of proteins with molecular weights lower than that of myosin heavy chain. Calpastatin levels were muscle-dependent and correlated with myofibrillar ATPase activity (r = -0.99). In a second experiment Mm rectus abdominis (RA) and psoas major (PM) of adrenalin-treated (n = 6) and control (n = 6) Friesian-Holstein calves were sampled at 1 and 29 h pm for assessment of calpain activities. At seven days pm the M longissimus (LO) was sampled for tenderness evaluation. pH values were measured at 30 min, 4 h and 29 h pm. Adrenalin treatment resulted in a higher ultimate pH in the three muscles. Higher ultimate pH resulted in lower calpain activities in the RA at 29 h pm (P less than or equal to 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

Utility of immunohistochemical identification of muscle proteins in microstructural studies of comminuted meat products

A series of experiments was conducted in an attempt to immunohistochemically identify specific muscle proteins in raw bovine muscle, meat batters and finely comminuted meat products. Three different antibodies were investigated-monoclonal anti-actin (IgG), polyclonal anti-desmin (IgG) and polyclonal anti-myoglobin (IgM). In addition, the fluorescent compound nitrobenzooxadiazole (NBD)-phallacidin was tested. The utility of the antibody anti-desmin proved to be poor. Anti-myoglobin and NBD-phallacidin were useful in muscle tissues that had been technologically treated to a limited extent. Anti-actin reacted with actin present in raw muscle tissue, in muscle samples comminuted with and without additives and in muscle samples that had been comminuted with additives and subsequently heated to 80°C and 115°C. However, its reactivity was markedly more distinct in raw than in processed samples. The utility of current immunohistochemical techniques to study the microstructure of processed meats seems to be limited due to the rapid denaturation of the specific muscle proteins.