The glycolytic
enzymes glycogen phosphorylase,
phosphofructokinase (PFK), and
pyruvate kinase (PK) were assessed in liver, heart, red muscle, and white muscle of aerobic and 5-h anoxic turtles (Pseudemys scripta) for changes in total activity and kinetic parameters.
Anoxia induced statistically significant changes in these glycolytic
enzymes in each of the four organs assayed. Compared with normoxic controls, anoxic liver showed a 3.3-fold increase in
glycogen phosphorylase activity, a 1.5-fold increase in the PFK I50 value for
citrate (concentration that inhibits initial activity by 50%), a 1.5-fold increase in the PFK Michaelis constant (Km) value for
fructose 6-phosphate (P), and an increased maximal activity of PK. Anoxic heart muscle showed a 2.6-fold decrease in
glycogen phosphorylase activity and, for PFK, a 1.7-fold decrease in the Km value for
ATP and a twofold increase in the I50 value for
citrate. In anoxic white muscle, PFK showed a fivefold lower Km value for fructose-6-P and a threefold lower activator concentration producing half-maximal activation (A50) for
potassium phosphate than the aerobic
enzyme form. Changes in anoxic white muscle PK included a twofold increase in the Km value for
ADP and a 1.7-fold decrease in the I50 value for
alanine. In red muscle,
anoxia affected only the Km value for
ATP, which was 50% higher than the value for the aerobic
enzyme form.
Fructose 2,6-diphosphate (P2) levels also decreased in heart muscle and increased in red and white muscle during
anoxia.(ABSTRACT TRUNCATED AT 250 WORDS)