Postmortem breakdown of ATP and glycogen in ground muscle: A review

The postmorte metabolism of ATP and glycogen in ground bovine muscle (in some cases also in rabbit muscle) was studied. At pH 7 protons released during postmortem glycolysis are bound by the phosphorylation of ADP to ATP and are liberated during enzymic hydrolysis of ATP. At lower pH values the protons are immediately released during glycolysis. Not more than 10% of the total drop in pH postmortem is due to protons liberated by the hydrolysis of ATP present in the tissue at death. Half of the buffering capacity of bovine muscle is caused by the myofibrillar proteins. The myofibrillar ATPases, rather than the membrane ATPases, seem to predominate in hydrolysing ATP postmortem in the intact as well as in the ground muscle. The rate of the breakdown of ATP determines the rate of postmortem glycolysis. Phosphofructokinase and, to a lesser extent, phosphorylase play the major role in the control of glycolytic metabolite levels in ground muscle. The mean values of glycogen recovery, obtained by measuring all glycolytic metabolites and lactate, indicate a general stoichiometric relationship in ground tissue, although several muscles did not fit in the scheme. Grinding of the prerigor muscle causes an accelerated hydrolysis of ATP and ADP, resulting in a faster increase in the IMP concentration and in an accelerated glycolysis. The increase in the turnover of ATP by grinding might be due to a faster release of Ca++ ions from the damage sarcoplasmic reticulum. Addition of sodium chloride (2–4%) to the ground pregidor muscle causes an increase in the rate of the breakdown of ATP to IMP. NaCl changes the steady-state of glycolysis without a major change in the rate of glycogen breakdown. The stimulation of phosphofructokinase observed is probably due to the faster disapearance of ATP in the presence of NaCl. The faster turnover of ATP could be due to an enhanced release of Ca++ ions from the sarcoplasmic reticulum by exchange against Na+ After several hours postmortem an inhibition of glycolysis occurs in the salted tissue which is probably due to a denaturation of glycolytic enzymes by the combined effect of low pH (<6) and high ionic strength. The high water-holding capacity of prerigor salted ground beef does not decrease postmortem in spite of the high rate of ATP breakdown. This effect can be explained by an inhibition of rigor mortis in the fibre fragments caused by the combined effect of ATP, high pH and salt ions. Addition of diphosphate to the prerigor ground tissue in the absence or presence of added NaCl results in an acceleration of ATP and glycogen breakdown. A hypothesis for the high ATP turnover is discussed. The higher rate of glycogen breakdown in the presence of diphosphate is caused mainly by an acceleration of the phosphofructokinase step. A rate limitation, by diphosphate, in the glyceraldehyde-3-phosphate dehydrogenase step and/or the following glycolytic steps was also observed.