Effect of sulphate on glutamate synthesis by intact spinach (Spinacia oleracea) chloroplasts.
During the course of NH4+ (or NO2-)-plus-alpha-oxoglutarate-dependent O2 evolution in spinach (Spinacia oleracea) chloroplasts, glutamate was continuously excreted out of the chloroplasts. Under these conditions, for each molecule of NO2- or NH4+ which disappeared, one molecule of glutamate accumulated in the medium and the concentration of glutamate in the stroma space was maintained constant. SO4(2-) (or SO3(2-) behave as inhibitors of NH4+ incorporation into glutamate by intact chloroplasts. This considerable inhibition of glutamate synthesis by SO4(2-) was correlated with a rapid decline in the stromal Pi concentration. The reloading of stromal Pi with either external Pi or PPi4- relieved SO4(2-)-induced inhibition of glutamate synthesis by intact chloroplasts. It was concluded that SO4(2-) induced a rapid efflux of stromal Pi out of the chloroplast, leading to a limitation of ATP synthesis and therefore to an arrest of ATP-dependent glutamine synthetase functioning.
Dumas
R
R
Laboratoire mixte CNRS/Rhône-Poulenc, Lyon, France.
Joyard
J
J
Douce
R
R
D001937:Brassica / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D005971:Glutamates / Q000096:biosynthesis*; D013431:Sulfates / Q000494:pharmacology*
D005971:Glutamates; D013431:Sulfates