-3-Carboxypropyl-l-cysteine specifically inhibits cystathionine γ-lyase-dependent hydrogen sulfide synthesis.

Hydrogen sulfide (HS) is a gaseous signaling molecule, which modulates a wide range of mammalian physiological processes. Cystathionine γ-lyase (CSE) catalyzes HS synthesis and is a potential target for modulating HS levels under pathophysiological conditions. CSE is inhibited by propargylglycine (PPG), a widely used mechanism-based inhibitor. In this study, we report that inhibition of HS synthesis from cysteine, but not the canonical cystathionine cleavage reaction catalyzed by CSE , is sensitive to preincubation of the enzyme with PPG. In contrast, the efficacy of -3-carboxpropyl-l-cysteine (CPC) a new inhibitor described herein, was not dependent on the order of substrate/inhibitor addition. We observed that CPC inhibited the γ-elimination reaction of cystathionine and HS synthesis from cysteine by human CSE with values of 50 ± 3 and 180 ± 15 μm, respectively. We noted that CPC spared the other enzymes involved either directly (cystathionine β-synthase and mercaptopyruvate sulfurtransferase) or indirectly (cysteine aminotransferase) in HS biogenesis. CPC also targeted CSE in cultured cells, inhibiting transsulfuration flux by 80-90%, as monitored by the transfer of radiolabel from [S]methionine to GSH. The 2.5 Å resolution crystal structure of human CSE in complex with the CPC-derived aminoacrylate intermediate provided a structural framework for the molecular basis of its inhibitory effect. In summary, our study reveals a previously unknown confounding effect of PPG, widely used to inhibit CSE-dependent HS synthesis, and reports on an alternative inhibitor, CPC, which could be used as a scaffold to develop more potent HS biogenesis inhibitors.