期刊
BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS
卷 1621, 期 2, 页码 226-233出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/S0304-4165(03)00073-4
关键词
glutathione S-transferase; non-covalent binding; protection; heme; protoporphyrinogen; tetrapyrrole
Glutathione S-transferases (GSTs) are multi-functional enzymes, known to conjugate xenobiotics and degrade peroxides. Herein, we report on the potential of four Zea mays GST isoforms (Zm GST I-I, Zm GST I-II, Zm GST II-II and Zm GST III-III) to act as binding and protection proteins. These isoforms bind protoporphyrin IX (PPIX), mesoporphyrin, coproporphyrin, uroporphyrin and Mg-protoporpyhrin, but do not form a glutathione conjugate. The binding is non-covalent and inhibits GSTs enzymatic activity, dependent on the type of the porphyrin and GST isoform tested. I-50 values are in the range of 1 to 10 muM for PPIX, the inhibition by mesoporphyrin and Mg-protoporphyrin (Mg-PPIX) is two to five times less. The mode of binding is non-competitive for the hydrophobic substrate and competitive for glutathione. Binding affinities (K-D values) of the GST isoforms are between 0.3 and 0.8 muM for coproporphyrin and about 2 muM for mesoporphyrin. Zm GST III-III prevents the nonenzymatic autoxidation of protoporphyrinogen to the phytotoxic PPIX. Zm GST II-II can reduce the oxidative degradation of hemin. This points to a specific ligand role of distinct GST isoforms to protect tetrapyrroles in the plant cell. (C) 2003 Elsevier Science B.V. All rights reserved.
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