Effects of serotonin (5-hydroxytryptamine) and adenosine 3',5'-phosphate on phosphofructokinase from the liver fluke Fasciola hepatica.

The stimulatory effect of serotonin on glucose uptake and lactic acid production in the parasitic trematode, the liver fluke, Fusciola hepatica, was reported previously (1). Subsequently, it was found that incubation of the intact liver fluke with serotonin results in an increase of glycolysis in cell:free homogenates (2). Evidence was presented indicating that this effect was partly due to an increase in the activity of phosphofructokinase, an enzyme which limits the rate of glycolysis in this organism. Increased activity of this enzyme seems to occur also in intact organisms, since the amount of the product of phosphofructokinase reaction, fructose diphosphate, was increased and the amount of the substrate, fructose g-phosphate, was reduced after exposure of the intact flukes to serotonin. Both serotonin and adenosine 3’,5’phosphate increased the activity of phosphofructokinase when added directly to liver fluke homogenate. Since it was reported before that serotonin increases the production of adenosine 3’) 5’phosphate in the fluke (3), the possibility then existed that activation of phosphofructokinase by serotonin could be mediated via the cyclic nucleotide. A similar situation exists in the activation of phosphorylase by epinephrine via the cyclic nucleotide (4, 5). This paper presents data relating to the influence of serotonin and of adenosine 3’,5’-phosphate on the activity of phosphofructokinase from the liver fluke and other sources. Other conditions which affect phosphofructokinase activity will also be reported. A preliminary report of some of this work has been given (6).