Degradation of L-Djenkolate Catalyzed by S-Alkylcysteine α,β-Lyase from Pseudomonas putida

Abstract

S-Alkylcysteine alpha, beta-lyase [EC 4.4.1.6] of Pseudomonas putida catalyzes alpha,beta-elimination of L-djenkolate [3,3'-methylenedithiobis(2-aminopropionic acid)] to produce pyruvate, ammonia, and S-(mercaptomethyl)cysteine initially. Secondly, S-(mercaptomethyl)-cysteine, which was identified in the form of S-(mercaptomethyl)cysteine thiolactone and S-(2-thia-3-carboxypropyl)cysteine in the absence and presence of iodoacetic acid, respectively, is decomposed enzymatically to pyruvate, ammonia, and bis(mercapto)methane, or spontaneously to cysteine, formaldehyde, and hydrogen sulfide. Balance studies showed that 1.3 mol each of pyruvate and ammonia and 0.2 mol each of formaldehyde and cysteine were produced with consumption of 1 mol of L-djenkolate. 1,2,4,5-Tetrathiane, 1,2,4-trithiolane, 1,2,4,6-tetrathiepane, and 1,2,3,5,6-pentathiepane, which are derivatives of bis(mercapto)methane, were also produced during the alpha,beta-elimination of L-djenkolate. In addition, a polymer with the general formula of -(CH2S)n- was produced as a white precipitate. When the alpha,beta-elimination of L-djenkolate was carried out in the presence of 20 mM iodoacetic acid, neither formaldehyde, cysteine, hydrogen sulfide, or the polymer were formed. Instead, the S-carboxymethyl derivatives of bis(mercapto)methane and S-(mercaptomethyl)cysteine were produced in addition to pyruvate and ammonia.