Comparison Between Different Assays for Superoxide Dismutase-Like Activity

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Abstract
The direct and indirect methods for assaying the superoxide dismutase activity of a compound are compared. With the use of a direct method, the mechanism of the catalysis of O2- dismutation by the tested compound can be determined, while with the indirect method it cannot, and this may lead to misinterpretation of the results. Assuming that the catalysis occurs via the 'ping-pong' mechanism, both the direct and indirect methods are limited to the determination of values of kcat greater than 10(5) M-1 s-1 and kcat greater than 3 x 10(6) M-1 s-1, respectively. Moreover, many side reactions may occur with the indirect method which may interfere with the measurements. Nevertheless, the indirect method approximates better the in vivo conditions than the direct method, and a tested compound that has high SOD activity using a direct method and low SOD activity using an indirect method, will most probably be a poor SOD mimic in vivo.