UNIT 4.36 Measurement of Cysteine S-Conjugate β-Lyase Activity

  1. Arthur J.L. Cooper1,
  2. Boris F. Krasnikov1,
  3. John T. Pinto1,
  4. Sam A. Bruschi2

Published Online: 1 MAY 2010

DOI: 10.1002/0471140856.tx0436s44

Current Protocols in Toxicology

Current Protocols in Toxicology

How to Cite

Cooper, A. J., Krasnikov, B. F., Pinto, J. T. and Bruschi, S. A. 2010. Measurement of Cysteine S-Conjugate β-Lyase Activity. Current Protocols in Toxicology. 44:4.36:4.36.1–4.36.18.

Author Information

  1. 1

    New York Medical College, Valhalla, New York

  2. 2

    Laural Consulting, Adelaide, Australia

Publication History

  1. Published Online: 1 MAY 2010
  2. Published Print: MAY 2010


Cysteine S-conjugate β-lyases are pyridoxal 5′-phosphate (PLP)–containing enzymes that catalyze the conversion of cysteine S-conjugates [RSCH2CH(NH3+)CO2] and selenium Se-conjugates [RSeCH2CH(NH3+)CO2] that contain a leaving group in the β position to pyruvate, ammonium and a sulfur-containing fragment (RSH) or selenium-containing fragment (RSeH), respectively. In mammals, at least ten PLP enzymes catalyze β-elimination reactions with such cysteine S-conjugates. All are enzymes involved in amino acid metabolism that do not normally catalyze a β-lyase reaction, but catalyze a non-physiological β-lyase side-reaction that depends on the electron-withdrawing properties of the –SR or –SeR moiety. In the case of cysteine S-conjugates, if the eliminated RSH is stable, the compound may be S-thiomethylated and excreted (thiomethyl shunt) or S-glucuronidated and harmlessly excreted. However, if RSH is chemically reactive, the cysteine S-conjugate may be toxic as a result of the β-lyase reaction. The cysteine S-conjugate β-lyase pathway is of particular interest to toxicologists because it is involved in the bioactivation (toxification) of halogenated alkenes and certain drugs. This unit provides protocols for the analysis of cysteine S-conjugate β-lyase activity. Curr. Protoc. Toxicol. 44:4.36.1-4.36.18. © 2010 by John Wiley & Sons, Inc.


  • ammonium;
  • cysteine S-conjugates;
  • cysteine S-conjugate β-lyases;
  • S-(1,2-dichlorovinyl)-l-cysteine;
  • S-(1,1,2,2-tetrafluoroethyl)-l-cysteine;
  • pyruvate