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Fructose 2,6-Bisphosphate and the Regulation of Pyrophosphate-Dependent Phosphofructokinase Activity in Germinating Pea Seeds ¹

Biochemistry Department, University of Georgia, Athens, Georgia 30602

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-P₂); however, the sensitivity of the enzyme's activity to fru 2,6-P₂ 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-P₂, while the small form shows a high sensitivity to this effector (K_a = 15 nanomolar). Gel filtration experiments indicate that fru 2,6-P₂ 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-P₂ is one mechanism for regulating glycolysis during seed germination.

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¹ Supported by the National Science Foundation through grant PCM-8023949.