Open AccessThe Structure of U17 Isolated from Streptomyces clavuligerus and its Properties as an Antioxidant Thiol
Author(s) -
Newton Gerald L.,
Bewley Carole A.,
Dwyer Tammy J.,
Horn Ronda,
Aharonowitz Yair,
Cohen Gerald,
Davies Julian,
Faulkner D. John,
Fahey Robert C.
Publication year - 1995
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1995.0821h.x
Subject(s) - chemistry , thiol , cysteine , moiety , stereochemistry , hydrolysis , biochemistry , enzyme
The predominant low‐molecular‐mass thiol produced by streptomycetes is a cysteine derivative previously designated as U17 [Newton, G. L., Fahey, R. C., Cohen, G. & Aharonowitz, Y. (1993) J. Bacteriol. 175 , 2734–2742]. In this study we report the elucidation of the structure of the monobromobimane derivative of U17, which establishes the structure of U17 as 2‐( N ‐acetylcysteinyl)amido‐2‐deoxy‐α‐ d ‐glucopyranosyl‐ myo ‐inositol. The presence of the N ‐acetylcysteine moiety was indicated by formation of N ‐acetylcysteine‐monobromobimane during acid hydrolysis of the monobromobimane derivative of U17. Complete hydrolysis released 1 mol glucosamine/mol cysteine as determined by carbohydrate and amino acid analysts. High‐resolution mass spectral analysis gave a precise mass consistent with the molecular formula C 27 H 40 N 4 O 14 S. Analysis of 13 C‐NMR, one‐dimensional 1 H‐NMR and two‐dimensional NMR experiments identified the remaining C 6 H 12 O 6 moiety as myo ‐inositol, confirmed the presence of N ‐acetyl‐cysteine and glucosamine, and established the connectivity of the components. Two chemical properties of this novel thiol make it suitable as an intracellular storage form of cysteine and as an antioxidant thiol. First, it undergoes heavy‐metal‐ion catalyzed autoxidation at a rate dramatically lower than that for cysteine and markedly lower than that for glutathione or N ‐acetylcysteine. Secondly, the α‐(1→1) glycosidic link between glucosamine and myo ‐inositol is resistant to acid hydrolysis, hydrolysing at a rate comparable to that of the two amide bonds in the molecule.