Arginase is a binuclear manganese metalloprotein that catalyses the hydrolysis of L-arginine to L-ornithine and urea. It is also regarded as a drug target for the treatment of asthma.  The mechanism of hydrolysis of L-arginine is carried out via nucleophilic attack on the guanidino group by water, forming a tetrahedral intermediate. Studies shown that a boronic acid moiety adopts a tetrahedral configuration and serves as an inhibitor.  In addition, the sulfonamide functional group can also mimic the transition state structure. Evidence of boronic acid mimics as transition state analogue inhibitors of human arginase I was elucidated by x-ray crystal structures.