CHARACTERIZATION OF PROTEINS UTILIZED IN THE DESULFURIZATION OF PETROLEUM-PRODUCTS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY

Matrix-assisted laser desorption ionization time-of-flight mass spectr ometry (MALDI/TOF/MS) with delayed extraction is utilized in linear, r eflected-ion and post-source decay (PSD) modes to directly characteriz e enzymes being developed for use in a petroleum desulfurization proce ss. The DNA sequence for the genes isolated from Rhodococcus sp. strai n IGTS8 that produce three of the four enzymes under study had been pr eviously reported with a discrepancy in residue assignments for one of the enzymes, dsz-C. The use of proteolytic digests followed by MALDI/ TOF/MS with delayed extraction in the reflected-ion mode provided sequ ence-specific information with mass accuracies exceeding 40 ppm over a range of masses and signal-to-noise values. Peptide mapping of >80% o f the residues was accomplished for all four proteins. The use of PSD established the true sequence for dsz-C, resolving the discrepancy in the literature. A posttranslational loss of N-terminal methionine was observed far each of the four proteins in linear MALDI/MS and was reco nfirmed by peptide mapping for three of the proteins. (C) 1998 Academi c Press.