title: Early post-mortem AMP-activated protein kinase (AMPK) activation leads to phosphofructokinase-2 and -1 (PFK-2 and PFK-1) phosphorylation and the development of pale, soft, and exudative (PSE) conditions in porcine longissimus muscle.
abstract: Pale, soft, and exudative (PSE) meat has been recognized for decades. Fast glycolysis during early post-mortem stage while the muscle temperature is still high is the cause of PSE meat. To elucidate the molecular mechanism underlying this fast glycolysis in muscle to become PSE meat, post-mortem ATP metabolism, fructose-2,6-diphosphate content, and the activities of AMPK, glycogen phosphorylase, and pyruvate kinase were examined in post-mortem muscle. Earlier and faster post-mortem AMPK activation was responsible for the significantly lower pH and higher lactic acid accumulation (p<0.05) seen in PSE muscle, which resulted in the occurrence of PSE meat. In muscle that became PSE meat, AMPK was activated at 0 h post-mortem and reached maximal activation at 0.5 h post-mortem, whereas AMPK reached maximal activation at 1 h post-mortem in the normal pork loin. Higher fructose-2,6-diphosphate content (p<0.05) was detected in PSE muscle compared to normal muscle at early post-mortem stage. However, no difference in the activities of glycogen phosphorylase and pyruvate kinase, rate-controlling enzymes in glycogenolysis and glycolysis, respectively, was detected between PSE and normal pork loins. Because fructose-2,6-diphosphate is a product of phosphofructokinase-2 (PFK-2), these data suggest that AMPK regulates post-mortem glycolysis through its phosphorylation and activation of PFK-2, which then up-regulates the activity of phosphofructokinase-1 (PFK-1), a key rate-controlling enzyme in glycolysis. Early AMPK activation in PSE muscle is associated with early consumption of ATP, because higher AMP and IMP contents and lower ATP content were detected in PSE meat compared to normal meat. Other mechanisms causing early AMPK activation in PSE meat may exist, which warrants further investigation.
authors.affiliation: Department of Animal Science, University of Wyoming, Laramie, Wyoming 82071, USA.
authors.forename: Qingwu W
authors.initials: QW
authors.lastname: Shen
authors.forename: Warrie J
authors.initials: WJ
authors.lastname: Means
authors.forename: Keith R
authors.initials: KR
authors.lastname: Underwood
authors.forename: Shane A
authors.initials: SA
authors.lastname: Thompson
authors.forename: Mei J
authors.initials: MJ
authors.lastname: Zhu
authors.forename: Richard J
authors.initials: RJ
authors.lastname: McCormick
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Ford
authors.forename: Mickel
authors.initials: M
authors.lastname: Ellis
authors.forename: Min
authors.initials: M
authors.lastname: Du
mesh_terms: D055372:AMP-Activated Protein Kinases; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D004789:Enzyme Activation; D005524:Food Technology; D008460:Meat; D009097:Multienzyme Complexes / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010732:Phosphofructokinase-1 / Q000378:metabolism*; D025481:Phosphofructokinase-2 / Q000378:metabolism*; D010766:Phosphorylation; D011180:Postmortem Changes; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011786:Quality Control; D013552:Swine
chemical_list: D009097:Multienzyme Complexes; D000255:Adenosine Triphosphate; D025481:Phosphofructokinase-2; D010732:Phosphofructokinase-1; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases