CHLOROPHYLL DEGRADATION IN Arabidopsis thaliana: DETECTION AND CHARACTERIZATION OF Mg-DECHELATASE ACTIVITY

BUCHERT AGUSTIN; CIVELLO PEDRO; MARTINEZ GUSTAVO

Pinamar, Argentina

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

SAIB

The enzymic release of Mg2+ 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 using the original substrate (chlorophyllide) as well as an artificial one (chlorophyllin). Enzyme activity was determined by measuring the increase in absorbance at 686 nm, the wavelength at which the Mg2+ release is detected. The enzyme showed an apparent Km of 0,127 (Abs686). The optimal temperature and pH were found at 55 °C and 7, respectively. The activity decreased considerably after heat treatment at 100 ºC for 5 minutes. 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