Carnosine enhances actomyosin-ATPase activity under acidic conditions: the role of carnosine in a rigor mortis.

Postmortem changes in skeletal muscle, particularly rigor mortis and the subsequent tenderization process, play a central role in determining meat quality and palatability. Proper progression of rigor mortis is essential, as its disruption leads to severe deterioration in meat texture and eating quality. Although the biochemical mechanisms underlying rigor mortis have been extensively studied, most investigations rely on simplified experimental systems and largely neglect the contribution of endogenous low-molecular-weight compounds present in muscle tissue. Imidazole dipeptides, such as carnosine, are abundant in skeletal muscle and are known to contribute to intracellular homeostasis through antioxidant and metal-chelating properties. Recently, these compounds have also been implicated in the regulation of calcium sensitivity in muscle contraction models. In the present study, we investigated the potential involvement of carnosine in rigor mortis by examining its effects on actomyosin ATPase activity under postmortem-like conditions. Under acidic and low-calcium conditions, which are unfavorable for actomyosin ATP hydrolysis, carnosine significantly enhanced ATPase activity. This enhancement was accompanied by increased tryptophan autofluorescence in the myosin head region upon ATP addition, suggesting an increased affinity between myosin and ATP. These findings indicate that carnosine facilitates the actomyosin ATPase cycle under postmortem conditions by enhancing calcium sensitivity and stabilizing ATP-myosin interactions. Our results suggest that endogenous carnosine contributes to the orderly progression of rigor mortis by promoting ATP depletion and contractile activity in postmortem skeletal muscle, providing new insight into the biochemical factors influencing meat quality and postmortem muscle behavior.