Collect. Czech. Chem. Commun. 1984, 49, 2698-2708

Regulation of proline-inhibitable glutamate kinase (EC, ATP: γ-L-glutamate phosphotransferase) of winter wheat leaves by monovalent cations and L-proline

Miroslav Štefl and Ludmila Vašáková

Department of Chemistry, Institute of Agriculture, 160 21 Prague 6-Suchdol


Proline-inhibitable glutamate kinase (GK1) of winter leaves is specifically regulated through feedback by L-proline during changes in the concentration of K+- and Na+- ions and in their ratio (K+/Na+). The enzyme is most active at 30 °C at a relatively high K+ + Na+ concentration and a K+/Na+ ratio of 1.8 to 10.2 and at 0 °C at both lower K+ + Na+ concentrations and a K+/Na+ ratio. An increase of the K+ + Na+ concentration to 1.25 mol/l and of the K+/Na+ ratio to 30.2 results in an activity decrease to one half; if, however, Na+ is increased to make K+/Na+ < 1, the activity becomes one tenth of that of the control. GK1 is completely inhibited through feedback by 50 mmol/l L-proline in the medium at pH 7.2 containing 207 + 40 mmol/l K+ + Na+; the inhibitin is switched off by increasing the K+ + Na+ concentration to the optimum, i.e. 357 + 40 mmol/l and this is the condition necessary for the start of L-proline biosynthesis. An additional increase of the K+ + Na+ concentration in the presence of L-proline results in complete inhibition of the enzyme. The changes in the activity of GK1 comply with the recorded data on the changes of L-proline accumulation in plats which parallel the changes of K+ and Na+ concentration in the nutrient medium. The theory of GK1 regulation by L-proline during changes in the ionic strength of the medium, which had been designed in the preceding work, was experimentally confirmed in this study.