Properties of Guaiacol Peroxidase Activities Isolated from Corn Root Plasma Membranes

Abstract

Although several investigations have demonstrated a plasma membrane (PM)-bound peroxidase activity in plants, this study is the first, to our knowledge, to purify and characterize the enzymes responsible. Proteins were extracted from highly enriched and thoroughly washed PMs. Washing and solubilization procedures indicated that the enzymes were tightly bound to the membrane. At least two distinct peroxidase activities could be separated by cation exchange chromatography (pmPOX1 and pmPOX2). Prosthetic groups were identified in fractions with peroxidase activity by absorption spectra, and the corresponding protein bands were identified by heme staining. The activities of the peroxidase enzymes responded different to various substrates and effectors and had different thermal stabilities and pH and temperature optima. Because the enzymes were localized at the PM and were not effected by p-chloromercuribenzoate, they were probably class III peroxidases. Additional size exclusion chromatography of pmPOX1 revealed a single activity peak with a molecular mass of 70 kD for the native enzyme, whereas pmPOX2 had two activity peaks (155 and 40 kD). Further analysis of these fractions by a modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with heme staining confirmed the estimated molecular masses of the size exclusion chromatography.

Naphthoquinone-Dependent Generation of Superoxide Radicals by Quinone Reductase Isolated from the Plasma Membrane of Soybean

“…Moreover, hydroquinones can be converted into semiquinones by these enzymes (Ohnishi et al, 1969). Plasma membranes isolated from maize roots were reported to contain at least two tightly bound guaiacol peroxidases (Mika and Lü thje, 2003). We tested aliquots (50 mg of protein) of our solubilized plasma membrane fraction with the assay used by these authors and found no detectable peroxidase activity.…”

Effect of Salinity Stress on Antioxidant Defense System of Niger (<i>Guizotia abyssinica</i> Cass.)

“…Salt stress induced ROS (H 2 O 2 ) in Niger seem to be primarily detoxified by POXs, as measured by GPOX and APX. GPOX, as a proven ROS quencher, is also associated with metabolism of plant hormones such as ethylene, indole acetic acid (IAA), and processes like cell wall lignification and wound healing [39]. Progressive elevation in GPOX up to 300 mM NaCl in parallel to H 2 O 2 levels appears to contribute to salt tolerance in niger (Figure 1).…”

The Stress of Suicide: Temporal and Spatial Expression of Putative Heat Shock Protein 70 Protect the Cells from Heat Injury in Wheat (Triticum aestivum)

“…Different isoforms of GPX and APX were observed in root and nodules of common bean under salt stress (Jebara and others 2005). GPX has been reported to show variations in activity in response to different substrates and has different thermal stabilities, pH, and temperature optima (Mika and Lüthje 2003). Peroxide scavenging enzymes-peroxidases and catalases-act on H 2 O 2 , whereas superoxide dismutase (SOD) is involved in converting ROS into peroxide radicals (Weydert and Cullen 2010).…”