Reactions are carried out in 50 mM Tris–HCl, pH 7.5, 5 mM MgCl2 and 100 mM NaCl using 2 µM cysteine desulfurase (Nfs) in presence or not of 2 µM SufE1. BSA 2 µM can be used as control. In addition to enzymes, pyridoxal 5′-phosphate (10 μM) and DTT (1 mM) are used for all reactions. Reaction is initiated by adding 500 μM L-cysteine for 30 min at 25°C. Then the reaction is quenched by adding 50 μl of 20 mM N,N-dimethyl-p-phenylenediamine dihydrochloride (prepared in 7.2 M HCl). The addition of 50 μl of 30 mM FeCl3 (prepared in 1.2 M HCl), followed by incubation for 20 min leads to formation of methylene blue, which is then measured at 670 nm. Na2S (1–100 μM) is used for calibration?

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