Fructose 2,6-Bisphosphate and the Regulation of Pyrophosphate-Dependent Phosphofructokinase Activity in Germinating Pea Seeds

THE ACTIVITY OF PYROPHOSPHATE: d-fructose-6-phosphate-1-phosphotransferase (EC 2.7.1.90, PPi-PFK) in cotyledons and sprouts of germinating pea seeds (Pisum sativum cv Alaska or Green Arrow) increases rapidly during the first 2 to 3 days after imbibition and then declines to a lower activity. The reaction toward fructose 1,6-bisphosphate formation is activated greatly by fructose 2,6-bisphosphate (fru 2,6-P(2)); however, the sensitivity of the enzyme's activity to fru 2,6-P(2) activation changes during germination.The cotyledon enzyme was partially purified and exists in two forms apparently with different molecular weights. The large form shows little sensitivity to fru 2,6-P(2), while the small form shows a high sensitivity to this effector (K(a) = 15 nanomolar). Gel filtration experiments indicate that fru 2,6-P(2) is involved in converting the small form into the large form. We propose that the interconversion of two forms of the PPi-dependent PFK by fru 2,6-P(2) is one mechanism for regulating glycolysis during seed germination.