Table IV. Estimation of in vivo molar mass-action ratios for different metabolic reactions in oilseed rape embryos.
The values of the molar mass-action ratios were calculated using the mean metabolite concentrations (Supplemental Table S5B), and the equations are given here. The respective theoretical equilibrium constant (Keq) for each reaction step is shown for comparison. Values that are displaced more than 10-fold from their respective Keq pinpoint irreversible reactions are indicated in boldface. Brackets indicate concentration.
| Enzyme Name | Calculated Mass-Action Ratio | Theoretical Keq |
|---|---|---|
| Suc synthase | ([Frc] × [UDP-Glc])/([Suc] × [UDP]) = 0.002 | 0.15 |
| UDP-Glc pyrophosphorylase | ([Glc-1-P] × [UTP])/[PPi] × [UDP-Glc]) = 23.2 | 3.2 |
| ADP-Glc pyrophosphorylase | ([ADP-Glc] × [PPi])/([Glc-1-P] × [ATP]) = 0.002 | 1 |
| Glucokinase | ([Glc-6-P] × [UDP])/([Glc] × [UTP]) = 0.06 | 873 |
| Fructokinase | ([Frc-6-P] × [UDP])/([Frc] × [UTP]) = 4.6 | 851 |
| Phosphoglucomutase | [Glc-1-P]/[Glc-6-P] = 0.34 | 0.05 |
| Phosphoglucoseisomerase | [Glc-6-P]/[Frc-6-P] = 3.52 | 0.5 |
| PFK | ([Frc-1,6-diP] × [ADP])/([Frc-6-P] × [ATP]) = 0.035 | 316 |
| Phosphoglycerate mutase, enolasea | [PEP]/[3-PGA] = 0.18 | 0.34 |
| Pyruvate kinase | ([Pyr] × [ATP])/([PEP] × [ADP]) = 12.3 | 327,119 |
a
The common intermediate 2-phosphoglycerate (2-PGA) was not measured. Equilibrium constants of phosphoglyceromutase and enolase were combined, allowing the ratio [PEP]-[3-PGA] to be derived (Supplemental Table S5B).