ABH ammonium salt is a strong and specific inhibitor of arginase and arginase II.

Arginase is the focal enzyme of the urea cycle catalyzing the hydrolysis of l-arginine to urea and l-ornithine. Emerging studies have identified arginase in the vasculature and have implicated this enzyme in the regulation of nitric oxide (NO) synthesis and the development of vascular disease. Upregulation of arginase inhibits endothelial NOS-mediated NO synthesis and may contribute to endothelial dysfunction in hypertension, ageing, ischaemia–reperfusion and diabetes. The induction of arginase may also promote aberrant vessel wall remodelling and neointima formation [1].

In vitro: 2(S)-amino-6-boronohexanoic acid (ABH) is inhibitor of type I arginase. At pH 7.5, ABH inhibited human type II arginase competitively with Ki value of 0.25 μM. However, at pH 9.5, ABH showed slow-binding inhibitory effects with Ki value of 8.5 nM [2].

In vivo: ABH enhanced both male and female sexual arousal responses in rabbits. In male rabbits received 150 μg ABH, the duration of the response increased by ~28%. In female rabbits received 4 or 6 mg/kg ABH, the inhibitor consistently potentiated the rise in genital tissue oxyhemoglobin concentration triggered by pelvic nerve stimulation. Inhibition of arginase is therefore a potential therapeutic target for the treatment of sexual arousal disorders [3].

References:[1].  Durante W, Johnson F K, Johnson R A. Arginase: a critical regulator of nitric oxide synthesis and vascular function[J]. Clinical and Experimental Pharmacology and Physiology, 2007, 34(9): 906-911.[2].  Colleluori D M, Ash D E. Classical and slow-binding inhibitors of human type II arginase[J]. Biochemistry, 2001, 40(31): 9356-9362.[3].  Cama E, Colleluori D M, Emig F A, et al. Human Arginase II: Crystal Structure and Physiological Role in Male and Female Sexual Arousal [J]. Biochemistry, 2003, 42(28): 8445-8451.