Effects of myosin heavy chain isoform composition on muscle fiber ATPase activity, postmortem metabolism, and meat quality in porcine muscle.

摘要

The overall purpose of this research was to determine the influence of myosin heavy chain (MyHC) isoform composition on the functionality of myofibrils in porcine muscle as it relates to postmortem energy metabolism and meat quality. The first study determined the influence of isolation method and pH decline on ATPase activity and MyHC isoform composition of myofibrils isolated from the red (RST) and white (WST) semitendinosus muscles at different times postmortem in electrically-stimulated (ES) and control (NS) carcasses. The MyHC isoform composition of isolated myofibrils was influenced by method of isolation and time postmortem, while myofibrillar ATPase activity was influenced by MyHC and muscle pH decline. The objective of the second study was to determine the influence of MyHC isoform composition on myofibrillar ATPase activity under simulated in vitro postmortem pH, Ca2+, and temperature conditions. ATPase activity and Ca2+-sensitivity of myofibrils decreased with pH. WST myofibrils had a greater ATPase activity but were less Ca 2+-sensitive than RST myofibrils. The objective of the third experiment was to determine the effect of MyHC isoform composition and pH on the inactivation susceptibility of the myofibrillar ATPase apparatus. In samples from both the RST and WST, a low muscle pH irreversibly inactivated the myofibrillar and actin-activated S1 ATPase activity. Actin binding to the S1 head was found to protect myosin from pH inactivation. MyHC isoforms were found to differentially influence the susceptibility to pH inactivation of actin-activated S1 ATPase activity. Using a histochemical ATPase assay and immunolocalization of MyHC isoform expression, the objective of the fourth study was to determine postmortem pH and temperature decline effects on the actomyosin ATPase activity of muscle fibers expressing different MyHC isoforms. Compared to slow muscle fibers, fibers expressing fast MyHC isoforms had a higher ATPase activity early postmortem but were more susceptible to ATPase inactivation by a rapid muscle pH decline. Overall these data suggest that MyHC isoform composition influences postmortem muscle ATP hydrolysis and susceptibility to protein alterations, which in turn affect postmortem metabolism and meat quality.