Denaturation of hake (Merluccius hubbsi) proteins was studied with DSC by monitoring T,,, of transitions and denaturation enthalpies. Whole muscle free of connective tissue showed two transitions (T,,,, 465°C and 75.3"C), and AH of 4.27 Cal/g. The exudative sarcoplasmic fraction showed three transitions (T,, 45.2"C, 59.O"C and 75.5"C) and AH of 3.92 Cal/g. The sarcoplasmic proteins from whole hake muscle contributed to both denaturation peaks. Muscle depleted of sarcoplasmic proteins by chloride extraction showed a higher thermal sensitivity and a diminished denaturation enthalpy on the second transition. This suggested an additional effect of chloride upon actin in addition to sarcoplasmic protein extraction. pH had an effect upon the native conformation of thick filament proteins, specifically myosin.

The biochemical properties and the characteristics of heat-induced gelation of natural actomyosin (NAM) from pre-and post-spawning hake were studied. 2+Mg ATPase activity, reduced viscosity and myosinl actin mole ratio of NAM from post-spawning fish were higher than those of pre-spawning ones. Gelation of both actomyosin at 10 mg mL-' of protein concentration was optimal at 60°C and pH 6.0. The highest rigidity was reached at 0.40M and 0.44M KC1 with NAM from pre-and post-spawning hake, respectively. Irrespective of heating temperature, ionic strength conditions and at pH range 5.5-7.5, rigidity of post-spawning hake NAM gels was higher than those of pre-spawning fish. Scanning electron micrographs of pre-and postspawning hake NAM showed "actin-type" and "myosin-type" ultrastructures, respectively.

We studied thermal denaturation of myofibrillar proteins from preand post-spawning hake by differential scanning calorimetry (DSC), and evaluated denaturation kinetics under both conditions. The denaturation enthalpies of all pre-spawning fish muscle extracts were less than those from post-spawning. The area under the DSC thermogram corresponding to myosin denaturation was smaller in myofibrillar extracts from pre-spawning than from post-spawning hake, while the areas corresponding to denaturation of actin were similar. Between 40 and 55°C the myosin denaturation rates were greater for postspawning than for pre-spawning hake. Both entalphies and kinetic data indicated proteins of fish in a better biological condition (postspawned) denature more rapidly and completely.

Cystic echinococcosis (CE) is a worldwide distributed helminthic zoonosis caused by Echinococcus granulosus. Benzimidazole derivatives are currently the only drugs for chemotherapeutic treatment of CE. However, their low efficacy and the adverse effects encourage the search for new therapeutic targets. We evaluated the in vitro efficacy of Bortezomib (Bz), a proteasome inhibitor, in the larval stage of the parasite. After 96 h, Bz showed potent deleterious effects at a concentration of 5 μM and 0.5 μM in protoscoleces and metacestodes, respectively (P < 0.05). After 48 h of exposure to this drug, it was triggered a mRNA overexpression of chaperones (Eg-grp78 and Eg-calnexin) and of Eg-ire2/Eg-xbp1 (the conserved UPR pathway branch) in protoscoleces. No changes were detected in the transcriptional expression of chaperones in Bz-treated metacestodes, thus allowing ER stress to be evident and viability to highly decrease in comparison with protoscoleces. We also found that Bz treatment activated the autophagic process in both larval forms. These facts were evidenced by the increase in the amount of transcripts of the autophagy related genes (Eg-atg6, Eg-atg8, Eg-atg12, Eg-atg16) together with the increase in Eg-Atg8-II detected by western blot and by in toto immunofluorescence labeling. It was further confirmed by direct observation of autophagic structures by electronic microscopy. Finally, in order to determine the impact of autophagy induction on Echinococcus cell viability, we evaluated the efficacy of Bz in combination with rapamycin and a synergistic cytotoxic effect on protoscolex viability was observed when both drugs were used together. In conclusion, our findings demonstrated that Bz induced endoplasmic reticulum stress, autophagy and subsequent death allowing to identify unstudied parasite-host pathways that could provide a new insight for control of parasitic diseases.