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

Abstract

The activity of pyrophosphate:D-fructose-6-phosphate-1-phosphotransferase (EC 2.7

Measurement of the Pyrophosphate Content of Plant Tissues

“…Other sources of PPi production are less well established. Although PPi-PFK is a reversible enzyme in vitro and could participate in gluconeogenesis in tissues such as castor bean endosperm which undergo a rapid conversion of fat to sugar (6), data on fru 2,6-P2-induced aggregation of PPi-PFK (14,15) and the kinetic characteristics of PPi-PFK (2, 13-15) support a glycolytic function for the enzyme. Fru 2,6-P2 promotes the association of a large molecular form of PPi-PFK which favors the glycolytic over the gluconeogenic direction of enzymic activity (14,15), and fru 2,6-P2 stimulates the glycolytic direction of PPi-PFK at lower concentrations than the gluconeogenic direction (13)(14)(15).…”

“…Although PPi-PFK is a reversible enzyme in vitro and could participate in gluconeogenesis in tissues such as castor bean endosperm which undergo a rapid conversion of fat to sugar (6), data on fru 2,6-P2-induced aggregation of PPi-PFK (14,15) and the kinetic characteristics of PPi-PFK (2, 13-15) support a glycolytic function for the enzyme. Fru 2,6-P2 promotes the association of a large molecular form of PPi-PFK which favors the glycolytic over the gluconeogenic direction of enzymic activity (14,15), and fru 2,6-P2 stimulates the glycolytic direction of PPi-PFK at lower concentrations than the gluconeogenic direction (13)(14)(15). Several workers indicate that fru 2,6-P2 is present in plant tissues in significant amounts (5,10,12,13) and its concentration fluctuates depending on parameters such as physiological condition of the plant (5,12) or physical factors such as light (10).…”

“…The discovery of a PPi-PFK2 in pineapple leaves (2) and the widespread distribution ofa high activity ofthis enzyme in many other plants (3,6,9,(13)(14)(15) raised the issue of whether plants contain PPi in sufficient amounts to support significant PPi-PFK activity. Theoretically, PPi is produced primarily during polymer synthesis reactions (e.g., DNA, RNA, cellulose, starch, sucrose, and the activation of amino acids and fatty acids).…”

“…Several workers indicate that fru 2,6-P2 is present in plant tissues in significant amounts (5,10,12,13) and its concentration fluctuates depending on parameters such as physiological condition of the plant (5,12) or physical factors such as light (10). Clearly, the glycolytic form of PPi-PFK, as indicated by fru 2,6-P2 (14,15), requires PPi as its substrate to function.…”

Fructose-2,6-bisphosphate Activates Pyrophosphate:d-Fructose 6-Phosphate 1-Phosphotransferase fromEuglena gracilis

“…PFP activity has been found in many plantsZ~6, 13,14) and the enzymes from K. MIYATAKE, T. ENOMOTO and S. KITAOKA The activity was assayed in the presence (0) and absence of 1JiM Fru-2,6-P2 (e). Fru-6-P was varied against a constant concentration of pyrophosphate (1 mM).…”