L-Arginine serves as a common substrate for both 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. BEC is a potent slow-binding competitive inhibitor of recombinant rat liver arginase I with a Ki of 0.4-0.6 µM. It is also a potent inhibitor of human arginase II with Ki values of 0.31 µM and 30 nM at pH 7.5 and 9.5, respectively. It does not inhibit murine iNOS at concentrations up to 1 mM. BEC significantly enhances NO-dependent relaxation of human penile corpus canvernosum smooth muscle in vitro at concentrations between 0.1-1.0 mM.