Reduction of ascorbate free radical by the plasma membrane of synaptic terminals from rat brain

• Published in: Archives of biochemistry and biophysics 2008-01, Vol.469 (2), p.243-254
• Main Authors: Samhan-Arias, Alejandro K., Duarte, Rui O., Martín-Romero, Francisco Javier, Moura, Jose J.G., Gutiérrez-Merino, Carlos
• Format: Article
• Language: English
• Subjects: Animals; Ascorbate; Ascorbate free radical; Ascorbic Acid - metabolism; Biochemistry - methods; Brain - metabolism; Cell Membrane - metabolism; Coenzyme Q; Coenzyme Q 1; Cytochrome c; Cytochromes c - metabolism; Edetic Acid - chemistry; Free Radicals; NADH oxidase; NADPH Oxidases - metabolism; Oxidation-Reduction; Rats; Synapses - metabolism; Synaptic plasma membranes; Ubiquinone - chemistry
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2007.10.004

Synaptic plasma membranes (SPMV) decrease the steady state ascorbate free radical (AFR) concentration of 1 mM ascorbate in phosphate/EDTA buffer (pH 7), due to AFR recycling by redox coupling between ascorbate and the ubiquinone content of these membranes. In the presence of NADH, but not NADPH, SPMV catalyse a rapid recycling of AFR which further lower the AFR concentration below 0.05 μM. These results correlate with the nearly 10-fold higher NADH oxidase over NADPH oxidase activity of SPMV. SPMV has NADH-dependent coenzyme Q reductase activity. In the presence of ascorbate the stimulation of the NADH oxidase activity of SPMV by coenzyme Q 1 and cytochrome c can be accounted for by the increase of the AFR concentration generated by the redox pairs ascorbate/coenzyme Q 1 and ascorbate/cytochrome c. The NADH:AFR reductase activity makes a major contribution to the NADH oxidase activity of SPMV and decreases the steady-state AFR concentration well below the micromolar concentration range.