The effect of temperature on the activity of μ- and m-calpain and calpastatin during post-mortem storage of porcine longissimus muscle

Phosphorylation inhibits the activity of μ-calpain at different incubation temperatures and Ca2+ concentrations in vitro

This study aimed to investigate the effects of phosphorylation on the activity of μ-calpain and its sensitivity to temperature and Ca²⁺. For temperature sensitivity analysis, sarcoplasmic protein was treated with alkaline phosphatase (AP) and phosphatase inhibitor (PI) at 4, 25 and 37°C. The results showed that the degradation degree of μ-calpain in the AP group was significantly higher after incubation for 12h. For calcium sensitivity analysis, samples treated with AP and PI were incubated at 0.01, 0.05, 0.1 and 1mM Ca²⁺. The results showed that the degradation rate of μ-calpain was maximum in the AP group and minimum in the PI group at 0.01, 0.05 and 0.1mM Ca²⁺. The differences between the three groups reduced as concentration increased. These data demonstrate that phosphorylation plays a negative role in regulating μ-calpain activity. This study clarifies the regulatory mechanism of μ-calpain activation in vitro and/or in postmortem muscle.

Postmortem muscle protein degradation in humans as a tool for PMI delimitation

Forensic estimation of time since death relies on diverse approaches, including measurement and comparison of environmental and body core temperature and analysis of insect colonization on a dead body. However, most of the applied methods have practical limitations or provide insufficient results under certain circumstances. Thus, new methods that can easily be implemented into forensic routine work are required to deliver more and discrete information about the postmortem interval (PMI). Following a previous work on skeletal muscle degradation in the porcine model, we analyzed human postmortem skeletal muscle samples of 40 forensic cases by Western blotting and casein zymography. Our results demonstrate predictable protein degradation processes in human muscle that are distinctly associated with temperature and the PMI. We provide information on promising degradation markers for certain periods of time postmortem, which can be useful tools for time since death delimitation. In addition, we discuss external influencing factors such as age, body mass index, sex, and cause of death that need to be considered in future routine application of the method in humans.

Postmortem degradation of skeletal muscle proteins: a novel approach to determine the time since death

Estimating the time since death is a very important aspect in forensic sciences which is pursued by a variety of methods. The most precise method to determine the postmortem interval (PMI) is the temperature method which is based on the decrease of the body core temperature from 37 °C. However, this method is only useful in the early postmortem phase (~0-36 h). The aim of the present work is to develop an accurate method for PMI determination beyond this present limit. For this purpose, we used sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, and casein zymography to analyze the time course of degradation of selected proteins and calpain activity in porcine biceps femoris muscle until 240 h postmortem (hpm). Our results demonstrate that titin, nebulin, desmin, cardiac troponin T, and SERCA1 degraded in a regular and predictable fashion in all samples investigated. Similarly, both the native calpain 1 and calpain 2 bands disintegrate into two bands subsequently. This degradation behavior identifies muscular proteins and enzymes as promising substrates for future molecular-based PMI determination technologies.

Calpain-1 activity in bovine muscle is primarily influenced by temperature, not pH decline

The objectives of this study were to 1) determine the conditions (temperature and pH) that exist in early postmortem muscle of normally chilled and delay chilled beef carcasses to provide a model for in vitro work and 2) determine the mechanism by which early postmortem temperature/pH conditions found in beef muscle influence the enzymes that regulate the aging process in vitro. For objective 1, 7 finished beef animals (HCW 385 ± 8 kg) were harvested with the right sides subjected to normal chilling (2.3°C) approximately 1.25 h postmortem and the left sides subjected to ambient temperature (delay chilling; 22.6°C) for an additional 4.75 h postmortem and then allowed to chill at 2.3°C. Delay chilled carcasses had a more rapid pH decline (P < 0.05) and a slower rate of carcass cooling (P < 0.05). No differences were observed between normally chilled and delay chilled samples for sarcomere length or postmortem proteolysis of troponin T (TnT; P > 0.10). Warner-Bratzler shear force (WBSF) was reduced in steaks from normally chilled carcasses at 14 d (P < 0.05), while results indicated a strong, positive correlation between 14-d WBSF and 3-h longissimus dorsi muscle (LM) temperature (r = 0.67, P < 0.01) as well as a strong, negative correlation between 14-d WBSF and 6-h LM pH (r = -0.65, P < 0.02). These results were used to design the methodology for objective 2, where isolated myofibrils were subjected to μ-calpain digestion at 4 or 22°C with either a fast or slow initial pH decline. As expected, digestions with a fast initial pH decline had lower pH values in the early time points of the incubation (P < 0.05). No differences were detected in μ-calpain activity or in the degradation of intact TnT between the fast and slow pH decline treatments (P > 0.10); however, warmer digestions resulted in a tendency for increased activation of μ-calpain (P < 0.10) and a significant reduction in intact TnT (P < 0.05). Additionally, a temperature × time interaction was revealed in μ-calpain activity and in the degradation of intact TnT (P < 0.05). Specifically, assayed calpain activity was lower at 0.17, 0.33, 1, and 3 h and greater at 72 h in warmer digestions, while intact TnT disappearance was greater as both time and digestion temperature increased. Meat aging and μ-calpain activity are influenced by both temperature and pH, but more research is necessary to fully realize their relationships.