Effects of elution [correction of eution] conditions on the separation of calpastatin, mu- and m-calpain on DEAE-Sephacel chromatography

Effect of electrical stimulation on protease activity and tenderness of M. longissimus from cattle with different proportions of Bos indicus content

The effect of electrical stimulation on protease activity (at approx. 3 h postmortem), sensory tenderness scores and shear force was determined on M. longissimus samples from three Bos indicus genotypes (0% Hereford, 50% Brahman×Hereford and 100% Brahman). The samples were divided and aged for 1 or 30 days. Electrical stimulation resulted in a general reduction in calpastatin activity suggesting that it accelerated proteolysis. Calpastatin activity increased commensurate with increasing Bos indicus content. Several significant interactions were shown, the most relevant of these was the interaction between Bos indicus content×electrical stimulation. In contrast to the other genotypes, calpain I and calpain II activities were shown to increase (significant for calpain II only) following stimulation in the purebred Brahmans (100%). There was a significant reduction in tenderness with increasing Bos indicus content. However, breed differences in shear force were reduced by electrical stimulation. The improvement in shear force following ageing was smaller for stimulated carcasses compared to the controls. This tends to reinforce the premise that electrical stimulation accelerates proteolysis. The results of this study show clear genotypic differences in proteolytic activity and tenderness. However, electrical stimulation can be employed to reduce breed differences in tenderness of the M. longissimus.

Purification and characterization of calpastatin from grass prawn muscle (Penaeus monodon)

Calpastatin, a specific calpain inhibitor was purified to electrophoretical homogeneity from grass prawn (Penaeus monodon) muscle by 100 degrees C heat-treatment, DEAE-Sephacel, and Q-Sepharose chromatographs. No significant change in the inhibitory activity of crude calpastatin was observed even after 20 min incubation at 100 degrees C, pH 7.0. The purified prawn calpastatin had a molecular weight (M(r)) of 80 and 88.7 kDa determined by SDS-PAGE and Sephacryl S-200 HR gel filtration, respectively. According to the active site titration, the purified calpastatin revealed four beef mu-calpain and two beef m-calpain binding domains, respectively. It was stable during 1 h of incubation at 30 degrees C under pH 4.5-10.0 and shown to be a highly specific inhibitor for calpain.