QUANTITATIVE ASPECTS OF THE IN VIVO REGULATION OF PYROPHOSPHATE - FRUCTOSE-6-PHOSPHATE 1-PHOSPHOTRANSFERASE BY FRUCTOSE-2,6-BISPHOSPHATE

摘要

Pyrophosphate:fructose-6-phosphate 1-phosphotransferase (PFP) was quantified in developing barley (Hordeum vulgare) leaves by immunostaining on western blots using a purified preparation of barley leaf PFP as standard. Fructose-2,6-bisphosphate (Fru-2,6-bisP) was quantified in the same tissues. Depending on age and tissue development, the concentration of PFP varied between 11 and 80 mu g PFP protein g(-1) fresh weight, which corresponds to 0.09 to 0.65 nmol g(-1) fresh weight of each of the alpha and beta PFP subunits. The level depends primarily on the maturity of the tissue. In the same tissues the concentration of Fru-2,6-bisP varied between 0.07 and 0.46 nmol g(-1) fresh weight. Thus, the concentrations of PFP subunits and Fru-2,6-bisP were of the same order of magnitude. In young leaf tissues the concentration of PFP subunits may exceed the concentration of Fru-2,6-bisP. This means that the amount of Fru-2,6-bisP present will be too low to occupy all the allosteric binding sites on PFP even though the concentration of Fru-2,6-bisP exceeds the K-a(Fru-2,6-bisP) by several orders of magnitude. These results are discussed in relation to Fru-2,6-bisP as a regulator of enzyme activities under in vivo conditions. [References: 21]