• Product name

    Cysteine Assay Kit (Fluorometric)
  • Detection method

  • Sample type

    Urine, Serum, Other biological fluids
  • Assay type

  • Sensitivity

    10 µM
  • Species reactivity

    Reacts with: Mammals, Other species
  • Product overview

    Cysteine Assay Kit (Fluorometric) (ab211099) provides a convenient method to quantify cysteine present in biological fluids such as serum and plasma. The assay principle is based on the cleavage of thiol group in reduced cysteine to produce that emits a stable signal that can be detected at Ex/Em = 365/450 nm. The amount of signal is directly proportional to the amount of total cysteine in the sample.

    The reaction is specific and other thiol-based amino acids do not interfere with the assay. The assay can detect as little as 10 µM of Cysteine in a variety of samples.

  • Notes

    Cysteine (CYS, C) is a sulfhydryl-containing amino acid, and is an important structural and functional part of proteins. In animals, cysteine is synthesized from trans-sulfuration of homocysteine (HCY), which is itself derived from metabolism of the amino acid methionine. The enzyme Cystathionine β-Synthase catalyzes condensation of homocysteine with serine to form cystathionine, which is deaminated and hydrolyzed by Cystathionine β-lyase to form cysteine and α-ketobutyrate. Due to its nucleophilic nature, the thiol group of cysteine has numerous biological functions. The formation of disulfide linkages between the thiol groups of cysteine residues helps to stabilize the tertiary and quaternary structure of proteins. Cysteine, homocysteine and other aminothiols exist in plasma in reduced, oxidized, and protein-bound forms, interacting with each other through redox pathways.

    Cysteine is the limiting precursor of the major intracellular antioxidant glutathione. The individuals with lower cysteine levels are more prone to damage from reactive oxygen species, which are generally removed either by thiols or by glutathione-linked enzymes. An elevated level of total cysteine also predicts adverse outcomes such as cardiovascular diseases and metabolic syndromes.

  • Platform

    Microplate reader


  • Storage instructions

    Store at -20°C. Please refer to protocols.
  • Components 100 tests
    CYS Assay Buffer 1 x 25ml
    CYS Probe 1 x 500µl
    CYS Standard (10 µmole) 1 vial
    Enzyme Mix I 1 x 50µl
    Enzyme Mix II (500 mg) 3 vials
    HCY Blocker 1 x 100µl
    Reducing Agent (20 mg) 2 vials
  • Research areas

  • Relevance

    Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins in small quantities. When exposed to air it oxidizes to form cystine, which is two cysteine molecules joined by a disulfide bond.
  • Alternative names

    • (2R) 2 amino 3 sulfanyl propanoic acid


  • Typical Cysteine standard calibration curve.

  • Kinetic curves showing estimation of Cysteine concentration present in human plasma. Calculated cysteine concentration in plasma following assay protocol is 251 ± 20 µM.



ab211099 has not yet been referenced specifically in any publications.

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