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    • In conclusions MPE effects in causing lesser

    2024-04-26

    In conclusions, MPE effects in causing lesser increase in vaginal fluid pH could partly restore the vaginal acidity in sex-steroid deficient state. MPE could exert its effect via enhancing both H+ generation as well as H+extrusion into the vaginal lumen. Although gallic 7915 is the main constituent in MPE, the involvement of rutin, myrecetin, quercetin and kaemferol in mediating these effects are likely due to their estrogen-like activities.
    Introduction During the conversion of muscle to meat, pH declines due to an accumulation of hydrogen ions (H+) in the muscle. This process is, in fact, the foundation of a unique set of characteristics on fresh meat, namely its ability to reflect light (color) and water holding capacity (Scheffler & Gerrard, 2007). While acidification of muscle via anaerobic glycolysis postmortem is indisputable, the biochemical mechanisms responsible for pacing this proton-mediated decline or arresting the process in such a metabolically complex tissue remain rather obscure. This lack of clarity has stalled, or rendered futile, attempts to develop technologies to predict meat quality early in the harvesting process so that greater product consistency can be managed (Henckel et al., 2002, Monin and Sellier, 1985, Scheffler et al., 2013). Though difficult to fathom, this lack of progress is likely due, in part, to the oversimplification of the scientific interpretation of postmortem metabolism and how it is controlled. Traditionally, postmortem muscle acidification has been attributed to the mobilization of stored muscle glycogen to lactate and H+ by anaerobic glycolysis. While muscle tissue undeniably experiences a loss of oxygen during the postmortem period, we have shown in multiple studies that mitochondria can significantly contribute to the rate and extent of postmortem metabolism (England et al., 2016, Matarneh et al., 2017, Scheffler et al., 2015). In our most recent study (Matarneh et al., 2017), we used an in vitro system to evaluate the contribution of mitochondria to postmortem metabolism. Our data revealed that intact mitochondria slowed (shouldered) the rate of pH decline through the first 30min by stabilizing ATP levels and reducing glycolytic flux. After 120min, however, mitochondria can also enhance glycogen degradation, ATP hydrolysis, lactate accumulation, and pH decline. After a series of experiments, we found that the causative agent for this enhanced glycolytic flux is a protein related to or closely associated with mitochondria. Therefore, the present study attempted to identify this causative protein. Mitochondrial ATP synthase is composed of two functional domains: the membrane-embedded domain, F0, which is responsible for proton translocation across mitochondrial inner membrane, and the soluble catalytic domain, F1, that extends into the matrix. During cellular respiration, protons are pumped from the matrix to the intermembrane space to generate a proton gradient across the inner membrane (membrane potential, Ψmt). The flow of protons back into the matrix through the F1F0 ATP synthase drives the synthesis of ATP. Because oxygen is the final electron acceptor in the electron transport chain (ETC), the lack of oxygen during the postmortem period halts the ETC and gradually decreases the Ψmt. As the postmortem period progresses, mitochondrial Ca and reactive oxygen species (ROS) levels continue to increase, promoting the formation of a mitochondrial permeability transition pore (mPTP) (Halestrap and Pasdois, 2009, Lomiwes et al., 2014). This event destroys the Ψmt, thereby causing the ATP synthase to function in reverse, consuming ATP in an attempt to conserve the Ψmt (St-Pierre, Brand, & Boutilier, 2000). Additional consumption of ATP by mitochondria has been proposed to promote postmortem metabolism (Hudson, 2012). Yet, our previous study (Matarneh et al., 2017) revealed that enhanced glycolytic flux was maintained in the presence of oligomycin, an inhibitor of ATP synthase that inhibits both ATP synthesis and hydrolysis. Even so, however, this does not rule out ATP synthase from being the causative agent, as the F1 domain can dissociate from the F0 domain and become oligomycin insensitive and act only as an ATPase (F1-ATPase) (Dubinsky, 1987, Foster and Fillingame, 1979, Gibson, 1983). Therefore, we hypothesized that mitochondrial F1-ATPase, more specifically its β-subunit, increases ATP hydrolysis and subsequently the flux through glycolysis. To test our hypothesis, we utilized Na-azide to inhibit the ATPase activity of the F1 domain (Ishii, Shirai, Makino, & Nishikata, 2014). We assumed that if F1-ATPase is the causative protein, then including Na-azide would reverse the observed effects.