Chlorophyll degradation in Arabidopsis thaliana: detection and characterization of Mg-dechelatase activity

PEDRO MARCOS CIVELLO; BÜCHERT A; MARTÍNEZ GA

Pinamar, Pcia. Buenos Aires

Congreso; 10th Congress of PABMB (Panamerican Association for Biochemistry and Molecular Biology); 2005

PABMB y SAIB

The enzymic release ofMg+2 from chlorophyllide, in the catabolic pathway of chlorophyll, has been demonstrated in higher plants as well as in algae, but detailed knowledge about the properties of Mg-dechelatase is scarce. MDS activity was detected in Arabidopsis thaliana leaves. Enzyme activity was determined by measuring the increase in absorbance at 686 nm, the wavelength at which the Mg+2 release is detected. The enzyme showed an apparent Km of 150 nM. The optimal temperature was found at 55°C and the optimal pH around 7.0. The activity decreased considerably after heat treatment (100°C, 10 minutes), although certain heat stability was detected. Variations in MDS activity during dark induced senescence in detached leaves were also determined. Activity increased constantly until reaching a maximum in day 4, after which it began decreasing. Purification through selective precipitation with ammonium sulfate was performed and the 40-90% fraction showed a considerably higher MDS activity than the crude extract.