Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

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.