Substrate Level Profiles of Metabolic Pathways in Frog Heart
223
activation of phosphorylase could be seen. After a 60 sec infusion, phosphofructokinase activation became more marked and was accompanied by
phosphorylase activation, as shown by the increase of G1P and G6P.
Glucose entry was further inhibited. The increase of the glycolytic flux at
60 and 120 sec is evident if we consider the strong increase of lactate and
pyruvate.
II
1
LIP 3060(112)
a-GPIDAP 148(055)
M/OAA5341 (1949)
{
ATP/ADP 3.96 (046)
PC/Cr 138(039)
1
L +P 14286 (5646)
PC+Cr 28540 (2950)
ATP+ADP+AMP
27570 (1542)
Fig. 1. Network of substrate levels and derived parameters in control frog hearts.
Inside the squares: mean values, m[Lmolesjg dry weight. Abbreviations used: see
Materials and Methods. Between the squares: mass-action ratios. For details,
see Materials and Methods. Standard deviations are given in brackets
Effect of ouabain (Fig. 3). After 30 sec, a clearly positive balance of
energy-rich phosphates was evident (increase of ATP, of ATP jADP- and
PC/Cr-ratios). Glycolysis was activated at the expense of glycogen: in
fact, glucose, G6P, pyruvate, lactate, and the sum: lactate + pyruvate were
increased. No activation of phosphofructokinase was evident. As already
reported [1], after a 60 sec injection a crossover point may be observed
within the glucokinase-phosphoglucomutase steps. After a 120 sec infusion,
the crossover is located at the phosphofructokinase-aldolase step. The direc-