A novel potentiometric biosensor for selective l-cysteine determination using l-cysteine-desulfhydrase producing Trichosporon jirovecii yeast cells coupled with sulfide electrode

• Published in: Analytica chimica acta Vol. 602; no. 1; pp. 108 - 113
• Main Authors: Hassan, Saad S.M., El-Baz, Ashraf F., Abd-Rabboh, Hisham S.M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 17.10.2007
• Subjects: Biosensing Techniques - methods; Biosensors; Cystathionine gamma-Lyase - metabolism; Cysteine - analysis; Cysteine - metabolism; Electrodes; Hydrogen-Ion Concentration; Initial slope method; l-Cysteine; l-Cysteine desulfhydrase enzyme; Pharmaceutical analysis; Potentiometry; Potentiometry - methods; Reproducibility of Results; Sensitivity and Specificity; Sulfide electrode; Sulfides - chemistry; Temperature; Time Factors; Trichosporon - enzymology; Trichosporon - metabolism; Trichosporon jirovecii yeast cells; l-Cysteine; l-Cysteine desulfhydrase enzyme; Sulfide electrode; Initial slope method; Pharmaceutical analysis; Biosensors; Potentiometry; Trichosporon jirovecii yeast cells
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2007.09.007

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 Ag 2S 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 °C and actual weight of immobilized yeast cells 100 mg), a linear relationship between l-cysteine concentration and the initial rate of sulfide liberation (d E/d t) is obtained. The sensor response covers the concentration range of 0.2–150 mg L −1 (1.7–1250 μmol 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 ∼1 μmol 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.