The autolysis of meat occurs with the active participation of lysosome enzymes-cathepsins and
calpains (Hope-Jones, 2010).
(i) Inactivation of endogenous proteases, especially
calpains (the most important being [micro]-calpain): these enzymes need a reducing substrate to carry out their action, given the presence of functional groups -SH (thiols) which are subject to oxidation; however, the role of this mechanism is debated, as some authors highlighted the marginal role of
calpains in meat tenderization [35, 72].
Greer, "Ubiquitous
calpains promote caspase-12 and JNK activation during endoplasmic reticulum stress-induced apoptosis," The Journal of Biological Chemistry, vol.
Murphy, "
Calpains, skeletal muscle function and exercise," Clinical and Experimental Pharmacology and Physiology, vol.
Enzymes such as caspases,
calpains, thrombin, and cathepsins cleave tau.[39] Experiments in vitro indicate that caspases 1, 3, 6, 7, and 8 can cleave tau at different sites, resulting in the generation of truncated tau species which are primed for subsequent phosphorylation.[40],[41]
Calpain activity is regulated by a calcium-dependent heat-stable inhibitor, calpastatin.
The
calpain superfamily is complex, and more than 25
calpains or calpain-like molecules have been discovered.
Calpains are a family of calcium-activated cysteine proteases that catalyze the limited proteolysis of a number of cellular proteins in eukaryotes [18, 19].
The calpastatin (CAST) which has been found in all the tissues that contain
calpains, is a specific inhibitor of
calpain enzymes (Lonergan et al., 2010).
This axonal disintegration process is mediated by the activation of calcium-dependent proteases, such as
calpains, that target cytoskeleton proteins, especially neurofilaments, for degradation (10).
Therefore, a greater proportion of oxidative fibers reflect in lower activity of
calpains, due to a larger amount of calpastatin, resulting in lower muscle degradation and originating a less tender meat (Koohmaraie, 1996).