H2S biogenesis by human cystathionine gamma-lyase leads to the novel sulfur metabolites lanthionine and homolanthionine and is responsive to the grade of hyperhomocysteinemia.
Although there is a growing recognition of the significance of hydrogen sulfide (H(2)S) as a biological signaling molecule involved in vascular and nervous system functions, its biogenesis and regulation are poorly understood. It is widely assumed that desulfhydration of cysteine is the major source of H(2)S in mammals and is catalyzed by the transsulfuration pathway enzymes, cystathionine beta-synthase and cystathionine gamma-lyase (CSE). In this study, we demonstrate that the profligacy of human CSE results in a variety of reactions that generate H(2)S from cysteine and homocysteine. The gamma-replacement reaction, which condenses two molecules of homocysteine, yields H(2)S and a novel biomarker, homolanthionine, which has been reported in urine of homocystinuric patients, whereas a beta-replacement reaction, which condenses two molecules of cysteine, generates lanthionine. Kinetic simulations at physiologically relevant concentrations of cysteine and homocysteine, reveal that the alpha,beta-elimination of cysteine accounts for approximately 70% of H(2)S generation. However, the relative importance of homocysteine-derived H(2)S increases progressively with the grade of hyperhomocysteinemia, and under conditions of severely elevated homocysteine (200 microm), the alpha,gamma-elimination and gamma-replacement reactions of homocysteine together are predicted to account for approximately 90% of H(2)S generation by CSE. Excessive H(2)S production in hyperhomocysteinemia may contribute to the associated cardiovascular pathology.
Chiku
Taurai
T
Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0606, USA.
Padovani
Dominique
D
Zhu
Weidong
W
Singh
Sangita
S
Vitvitsky
Victor
V
Banerjee
Ruma
R
D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D002384:Catalysis; D003542:Cystathionine gamma-Lyase / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006862:Hydrogen Sulfide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D020138:Hyperhomocysteinemia / Q000378:metabolism*; D007700:Kinetics; D013058:Mass Spectrometry; D008956:Models, Chemical; D011994:Recombinant Proteins / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D013696:Temperature
D011994:Recombinant Proteins; D013440:Sulfides; D013455:Sulfur; D003542:Cystathionine gamma-Lyase; C001520:lanthionine; D003545:Cysteine; D000409:Alanine; D006862:Hydrogen Sulfide