Abstract
A chlorophyllide a breaching enzyme extracted from degreening Citrus unshiu fruits was purified some 1, 000-fold and characterized.1. The enzyme catalyses chlorophyllide a degradation in the presence of H2O2 and the phenols, 2, 4-dichlorophenol or p-coumaric acid. It behaves as a protein with a MW of 42, 000 on Sephacryl S-200 gel filtration but it does not give a single band on polyacrylamide gel electrophoresis (PAGE), SDS-PAGE, and upon staining with guaiacol in the presence of H2O2. The Michaelis constant, Km, for chlorophyllide a was 13.2 μM.2. The enzyme exhibited IAA oxidase activity in the presence of Mn++; it was inhibited by hydroquinone, Tiron, potassium cyanide (KCN), diethyldithiocarbamate (DIECA) but not by iodoacetate, p-chloromercuribenzoate (PCMB), N-ethylmaleimide, histidine, D-mannose, dimethylfuran, triethylenediamine, ethylenediaminetetraacetic acid (EDTA), NaN3 and thiourea.The possible in vivo participation of this in vitro enzyme system as a H2O2-scavenging system in the dark is discussed.
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