title: A novel potentiometric biosensor for selective L-cysteine determination using L-cysteine-desulfhydrase producing Trichosporon jirovecii yeast cells coupled with sulfide electrode.
abstract: Trichosporon jirovecii yeast cells are used for the first time as a source of L-cysteine desulfhydrase enzyme (EC 4.4.1.1) and incorporated in a biosensor for determining L-cysteine. The cells are grown under cadmium stress conditions to increase the expression level of the enzyme. The intact cells are immobilized on the membrane of a solid-state Ag2S electrode to provide a simple L-cysteine responsive biosensor. Upon immersion of the sensor in L-cysteine containing solutions, L-cysteine undergoes enzymatic hydrolysis into pyruvate, ammonia and sulfide ion. The rate of sulfide ion formation is potentiometrically measured as a function of L-cysteine concentration. Under optimized conditions (phosphate buffer pH 7, temperature 37+/-1 degrees C and actual weight of immobilized yeast cells 100 mg), a linear relationship between L-cysteine concentration and the initial rate of sulfide liberation (dE/dt) is obtained. The sensor response covers the concentration range of 0.2-150 mg L(-1) (1.7-1250 micromol L(-1)) L-cysteine. Validation of the assay method according to the quality control/quality assurance standards (precision, accuracy, between-day variability, within-day reproducibility, range of measurements and lower limit of detection) reveals remarkable performance characteristics of the proposed biosensor. The sensor is satisfactorily utilized for determination of L-cysteine in some pharmaceutical formulations. The lower limit of detection is approximately 1 micromol L(-1) and the accuracy and precision of the method are 97.5% and +/-1.1%, respectively. Structurally similar sulfur containing compounds such as glutathione, cystine, methionine, and D-cysteine do no interfere.
authors.affiliation: Department of Chemistry, Faculty of Science, Ain Shams University, Cairo, Egypt. saadsmhassan@yahoo.com
authors.forename: Saad S M
authors.initials: SS
authors.lastname: Hassan
authors.forename: Ashraf F
authors.initials: AF
authors.lastname: el-Baz
authors.forename: Hisham S M
authors.initials: HS
authors.lastname: Abd-Rabboh
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D003542:Cystathionine gamma-Lyase / Q000378:metabolism*; D003545:Cysteine / Q000032:analysis* / Q000378:metabolism*; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D011199:Potentiometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013440:Sulfides / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014250:Trichosporon / Q000201:enzymology* / Q000378:metabolism
chemical_list: D013440:Sulfides; D003542:Cystathionine gamma-Lyase; D003545:Cysteine