Postmortem regulation of glycolysis by 6-phosphofructokinase in bovine M. Sternocephalicus pars mandibularis

• Published in: Meat science 2005-08, Vol.70 (4), p.621-626
• Main Authors: Rhoades, Ryan D., King, D. Andy, Jenschke, Blaine E., Behrends, Jason M., Hively, Teresa S., Smith, Stephen B.
• Format: Article
• Language: English
• Subjects: 6-Phosphofructokinase; beef carcasses; beef quality; Biological and medical sciences; Bovine; enzymatic hydrolysis; enzyme activity; Food industries; Fundamental and applied biological sciences. Psychology; glycogen; glycogenolysis; glycolysis; lactates; mandibular glands; Meat and meat product industries; Metabolism; Postmortem muscle; rigor mortis; sarcoplasmic reticulum
• ISSN: 0309-1740; 1873-4138
• DOI: 10.1016/j.meatsci.2005.01.024

This experiment addressed the hypothesis that 6-phosphofructokinase (6-PFK) regulates glycolysis in postmortem in M. sternocephalicus pars mandibularis. In two separate experiments, muscle samples were excised from randomly-selected steers that would typically be found on a commercial slaughter floor. In the first experiment, two samples were obtained from each of 6 steers immediately post-exsanguination; one sample was immersed immediately in liquid nitrogen and the other was stored at 4 °C for 4 d, to compare 6-PFK enzyme activity and glycolytic intermediate concentrations between fresh and d 4 postmortem samples. The greatest activity of 6-PFK was measured in fresh muscle extracts at pH 7.4, whereas little activity was detectable at pH 7.0. 6-PFK activity measured at pH 7.4 in d 4 samples also was barely detectable. Hill coefficient values for 6-PFK in fresh samples measured at pH 7.4 or 7.0, and d 4 samples measured at pH 7.4 were 2.9, 0.8, and 0.7, respectively, indicating loss of cooperativity with both lowered pH during assay and with time postmortem. Glycogen concentrations decreased 45% from d 0 to d 4, to 39.6 μmol glycogen/g muscle. Muscle concentrations of free glucose increased ( P < 0.001) from 0.84 μmol/g at d 0 to 6.54 μmol/g at d 4. Fructose-6-phosphate and glucose-6-phosphate increased ( P < 0.001) from d 0 to d 4 (2.8-fold and 4.7-fold, respectively). Lactate began accumulating immediately (3.33 μmol/g) and was elevated to 45.9 μmol/g by d 4. In the second experiment, conversion of [U- 14C]glucose to lactate, glycogen, and CO 2 was measured in vitro at pH 7.4 and 7.0 in fresh M. sternocephalicus pars mandibularis strips from four steers. Total [U- 14C]glucose was less in muscle strips incubated at pH 7.0 than in those incubated at pH 7.4 (55.5 vs. 123 nmol glucose utilized per 100 mg muscle per h; P = 0.04), due primarily to a reduction in glucose conversion to lactate. The conversion of glucose to glycogen or CO 2 in vitro was unaffected by media pH. These results suggest that the postmortem decline in pH in M. sternocephalicus pars mandibularis ultimately inactivates 6-PFK; this occurs prior to the depletion of glycogen reserves.