Pyrophosphate: D-fructose-6-phosphate 1-phosphotransferase (PFP) Activities in Response to Fructose-2,6-P2 in Illuminated and Darkened Pineapple Leaves.

Abstract

Regulatory properties of Fru-2,6-P2 on pyrophosphate: D- fructose-6-phosphate 1-phosphotransferase [diphosphate- fructose-6-phosphate 1-phosphotransferase] (PFP; EC 2.7.1.90), its molecular weight and subunit structure in illuminated and darkened pineapple (Ananas comosus cv. Smooth-cayenne N67-10) leaves were investigated. Polyacrylamide gel electrophoresis and immunoblot revealed two subunits, alpha (66 kDa) and beta (64.1 kDa), in desalted leaf extracts. Diurnal PFP activity of pineapple showed the dependency on a day/night regulation. Glycolytic activity of PFP was dependent on pH, the degree of activation by Fru-2,6-P2 at pH 6.4 increased 4.16- and 11.13- fold during the day and night-time, respectively. However, gluconeogenic reaction was only weakly affected by Fru-2,6-P2 at various pH levels. PFP activity was also strongly dependent on temperature. In 10-40 deg C temperature regimes, glycolytic reaction of PFP activity showed about 2-fold activation by Fru- 2,6-P2 in both day and night, but gluconeogenic reaction was weakly affected. In both reactions, the PFP activity of darkened leaves was always lower than that of the day form. This suggested that nocturnal acidification of CAM in pineapple had significant effect on PFP. Results suggest that only a part of regulation of pineapple PFP was associated with Fru-2,6-P2, but some other factors were also responsible for PFP regulation.