L-Arginine serves as a common substrate for both nitric oxide synthase (NOS) and arginase in the cell.
L-Arginine serves as a common substrate for both nitric oxide synthase (NOS) and arginase in the cell. NOS catalyzes the oxidation of arginine to citrulline and NO with Nω-hydroxy-L-arginine (NOHA) formed as an intermediate. Arginase, on the other hand, catalyzes the hydrolysis of arginine into urea and L-ornithine. Thioarginine (hydrobromide) is a colorimetric substrate for arginase that provides the basis for continuous spectrophotometric measurement of enzyme activity. It exhibits Km and kcat values of 0.5 mM and 18,000 min-1, respectively, which are similar to physiological substrate arginine. The thiol product of the reaction reacts with DTNB to produce 2-nitro-5-thiobenzoate for easy visualization at 405-420 nm.
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