Stromal Free Calcium Concentration and Light-Mediated Activation of Chloroplast Fructose-1,6-Bisphosphatase 1
AUTOR(ES)
Kreimer, Georg
RESUMO
Light-mediated activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) in intact spinach chloroplasts (Spinacia oleracea L.) is enhanced in the presence of 10−5 molar external free Ca2+. The most pronounced effect is observed during the first minutes of illumination. Ruthenium red, an inhibitor of light-induced Ca2+ influx, inhibits this Ca2+ stimulated activation. In isolated stromal preparations, the activation of fructose-1,6-bisphosphatase is already enhanced by 2 minutes of exposure to elevated Ca2+ concentrations in the presence of physiological concentrations of Mg2+ and fructose-1,6-bisphosphate. Maximal activation of the enzyme is achieved between 0.34 and 0.51 millimolar Ca2+. The Ca2+ mediated activation decreases with increasing fructose-1,6-bisphosphate concentration and with increasing pH. The data are consistent with the proposal that the illumination of chloroplasts leads to a transient increase of free stromal Ca2+. In dark-kept chloroplasts the steady-state concentration of free stromal Ca2+ is 2.4 to 6.3 micromolar as determined by null point titration. These observations support our previous proposal that light-induced Ca2+ influx into chloroplasts does not only influence the cytosolic concentration of free Ca2+ but also regulates enzymatic processes inside the chloroplast.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1054500Documentos Relacionados
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