POST‐MORTEM GLYCOLYSIS IN OX SKELETAL MUSCLE: EFFECTS OF MINCING AND OF DILUTION WITH OR WITHOUT ADDITION OF ORTHOPHOSPHATE

Abstract

ABSTRACT— The rates of pH fall and of changes in glycolytic intermediates and cofactors in ox sternomandibularis muscle minced soon after slaughter were compared with the rates in unminced muscle. Mincing caused about a three‐fold increase in the rates of most of the post‐mortem changes but a much greater increase in the rate of loss of nicotinamide‐adenine dinucleotide (NAD). Glycolysing muscle minces were diluted with 1 vol of a solution containing potassium chloride, with or without added potassium phosphate. Increasing the potassium chloride concentration resulted in a higher ultimate pH of the diluted preparation, whereas inclusion of inorganic phosphate (Pi) in 0.16M potassium chloride solutions resulted in lower ultimate pH values, the maximum effect being obtained usually with 50 mM Pi in the diluent. The ultimate pH was then about the same as in the undiluted mince, provided that glycogen was not exhausted. Comparisons were made of the glycolytic metabolism in undiluted minces and in minces diluted with 0.16M potassium chloride containing 0, 50 or 100 mM potassium phosphate (pH 6.7). Dilution without addition of Pi decreased the glycolytic resynthesis of adenosine triphosphate (ATP) without affecting the initial adenosine triphosphatase (ATPase) activity. Consequently ATP was lost faster, metabolism caused sooner and the ultimate pH was higher than in the undiluted mince. Inclusion of Pi in the diluent stimulated the glycolytic resynthesis of ATP without affecting the initial ATPase activity. Consequently loss of ATP was delayed until, due to loss of NAD, the glyceraldehyde‐3‐phosphate dehydrogenase step became rate‐limiting for lactate production and fructose‐1,6‐diphosphate and the triose phosphates accumulated. Phosphorylase, phosphofructokinase and ATPase activities were calculated from the changes in glycolytic products and intermediates, and ‘high‐energy’ phosphates. Reasons are discussed for the differences in the activities of these enzymes among the different types of preparation.