Monday, May 4, 2009
5-19
Multi-mode Spectroscopic High Throughput Screening (HTS) of Phenols and Monolignols
Komandoor E. Achyuthan1, Blake A. Simmons2, Paul D. Adams3, and Anup Singh3. (1) Technology Division, Joint BioEnergy Institute (JBEI), 5885 Hollis Street, Emeryville, CA 94608, (2) Energy Systems, Sandia National Laboratories, 7011 East Avenue, Livermore, CA 94551, (3) Joint Bioenergy Institute, 5885 Hollis Street, Fourth Floor, Emeryville, CA 94608
Phenolic structure is a common motif amongst monolignols. We developed multi-mode, high throughput screening (HTS)-compatible, UV-Vis and fluorescence assays for phenols and monolignols that are executed in optical “turn on” or “turn off” formats and operated under kinetic or endpoint modes. We used p-cresol as a model phenol and coniferyl alcohol as a prototype monolignol. We chose Trametes versicolor fungal laccase to oxidize p-cresol and coniferyl alcohol and thus expanded the spectroscopic tools for analyzing these molecules. Laccase activity toward p-cresol was monitored kinetically at pH 4.5 by absorption changes at 250, 274 or 297nm, and in endpoint mode by a bathochromic shift to 326nm. Laccase oxidation of p-cresol was also detected by product fluorescence at 425nm after excitation at 262 or 322nm. We optimized the kinetic parameters for p-cresol oxidation (pH optimum 4.5-5.1; 37oC; Km = 2.2mM) resulting in laccase limits of detection and quantization (LOD, LOQ) of 25 and 75pg/mL, respectively. The p-cresol LOD was 8 micromolar. We similarly characterized the spectroscopic properties of coniferyl alcohol. Three isosbestic wavelengths were identified at 240, 242 and 262nm with S/B of ~50 for 500 micromolar coniferyl alcohol, establishing assay sensitivity. Coniferyl alcohol excitation spectrum (270 – 335nm) overlapped with its absorption spectrum. Fluorescence emission was between 360 – 500nm with peak at 416nm yielding 1 micromolar detection sensitivity. Unlike p-cresol, laccase oxidation of coniferyl alcohol quenched the fluorescence. In conclusion, orthogonal interrogation and ratiometric analysis capabilities of our assay enable high specificity while minimizing interferences during compound library screenings.