EVIDENCE FOR THE SHORT-TERM REGULATION OF GLYCOLYTIC FLUX IN THE ISOLATED-PERFUSED VENTRICLE OF THE LAND SNAIL HELIX-LUCORUM (L.) AFTER TREATMENT WITH SEROTONIN (5-HYDROXYTRYPTAMINE)
B. Michaelidis et E. Vasiliou, EVIDENCE FOR THE SHORT-TERM REGULATION OF GLYCOLYTIC FLUX IN THE ISOLATED-PERFUSED VENTRICLE OF THE LAND SNAIL HELIX-LUCORUM (L.) AFTER TREATMENT WITH SEROTONIN (5-HYDROXYTRYPTAMINE), Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 167(7), 1997, pp. 508-516
The glycolytic flux and the regulation of phosphofructokinase (PFK) ac
tivity by fructose 2,6-bisphosphate and covalent modification was inve
stigated in isolated ventricles of land snail Helix lucorum perfused w
ith or without serotonin. Serotonin evoked a significant increase in t
he level of glycolytic intermediates and a threefold increase of glyco
lytic flux. Studies of saturation curves of PFK for the substrate fruc
tose 6-phosphate at pH similar to intracellular pH of heart muscle sho
wed that serotonin increases enzyme sensitivity to activation by fruct
ose 6-phosphate. Moreover, PFK preparations from ventricles perfused w
ith serotonin exhibited lower K-a values for the activators AMP and fr
uctose 2,6-bisphosphate, compared with the enzyme preparations from se
rotonin-untreated ventricles. The results suggest that PFK was convert
ed to a more active form when exposed to serotonin. In vitro experimen
ts of PFK phosphorylation showed that the conversion of the enzyme to
a more active form was possibly due to its phosphorylation by an endog
enous cyclic-AMP-dependent protein kinase. The concentration of fructo
se 2,6-bisphosphate increased in serotonin-treated ventricles and it e
xerted a synergistic effect with AMP on the activation of PFK. The bou
nd fraction of glycolytic enzymes increased in the serotonin-treated v
entricles only after the 4th min of perfusion. The results suggest tha
t the stimulation of glycolytic flux in the ventricles of H. lucorum i
n the first minutes of perfusion with serotonin was partly due to the
activation of PFK via enzyme molecule covalent modification and to inc
rease of fructose 2,6-bisphosphate.