The research into the activity of tissue enzymes were also assessed - with regards to cathepsins and calpains
- in the muscular fiber of red deer meat.
This may be related to a lower proteolysis due to the reduced development of proteolytic bacteria, or to a more pronounced acidification of the substrate, thus decreasing the calpains
action (which mainly acts in a neutral environment) .
Yuan, "Cross-talk between two cysteine protease families: activation of caspase-12 by calpain
in apoptosis," The Journal of Cell Biology, vol.
Long-lasting Ca2+ elevations activate calpain
proteases, which further degrade proteins that participate in Ca2+ homeostasis and thereby aggravate myoplasmic Ca2+ overload.
Other enzymes involved in tau cleavage include asparagine endopeptidase (AEP) and caspase 2. AEP can cleave endogenous tau at Asn255 and Asn368 independently of caspases and calpains
, generating neurotoxic fragments that form insoluble fibrils in vitro . Caspase 2 cleaves tau at Asp314 generating a truncated 35 kDa fragment, which mislocalizes to dendritic spines, and also aberrantly promotes mislocalization of endogenous tau to spines.
In brief, it has been hypothesized that, under physiological conditions, inactive calpains
are stored in cellular cytosol and bound in a substrate competitive manner to their endogenous inhibitor calpastatin.
Increased intracellular [Ca.sup.2+] concentration has been linked to muscle damage, mitochondrial swelling, and degeneration of myofibrils, [57-59] and activation of calpains
, one of the most important nonlysosomal classes of proteases in skeletal muscle fibers, is indeed activated by increased [Ca.sup.2+] levels [60-62] and by excessive oxidative stress [34, 63, 64].
are involved in multiple cellular processes such as cell migration, actin cytoskeleton remodeling, and apoptosis .
are ubiquitously expressed in the central and peripheral nervous systems and are broadly activated when the intracellular calcium concentration rises to a standard level threshold (11).
In agreement with Shackelford, Morgan, Cross and Savell (1991), several studies demonstrate the influence of pH on the activity of cathepsins and calpains
, which are proteolytic enzymes, suggesting that the observed differences in pH may be partially responsible for the differences in tenderness.
Proteolytic enzymes such as cathepsins and calpains
are involved in structural and biochemical changes during post mortem ageing process (Ouali et al., 2005; Etherington et al., 1990; Oualiet al., 2006).The role of calpains
in meat tenderness has been extensively established (Delgado et al., 2001; Veiseth and Koohmaraie 2005).