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ANALYTICAL CURRENTS
Automated MS sequencing of unknown proteins Old habits are hard to break. Despite the advances in protein analysis by MS and its popularity as a means of identifying known proteins, the method of choice for sequencing unknown proteins (so-called de novo seTandem MS of 80 fmol BSA loaded on a gel, analyzed (A) on the QqTOF and (B) on a triple quencing) is still Edman degraquadrupole. (Adapted with permission. Copyright 1997 John Wiley & Sons.) dation. Matthias Mann and colleagues at the European Molecular Biolter than 50 ppm. The resolution and S/N of Unknown proteins were digested in ogy Laboratory (Germany), the University the QqTOF were much better than the trithe presence of 180 water and sequenced of Manitoba (Canada), and PE SCIEX ple quadrupole used for comparison. How- by a computer algorithm. Automated se(Canada) demonstrated that the combina- ever, the authors pointed out that a weakquence assignments—made after manual tion of nanoelectrospray 180 end labeling ness of the QqTOF is that it cannot perform assignment but before the gene seof peptides and a quadrupole/iime-ofparent ion scans. quences were known—yielded exact flight instrument quickly sequences gelThey expected that the improved reso- matches in two of the three examples. separated proteins The third peptide resulted in two mislution and mass accuracy would increase matches—a pair of reversed amino acids the specificity of peptide database To demonstrate the performance of the and a case in which the manual assignsearches and demonstrated this result by quadrupole/time-of-flight hybrid (which searching the databases with the sequenc- ment had been incorrect. At least partial they called a QqTOF), they analyzed automation of novel protein sequencing 80 fmol bovine serum albumin (BSA) sam- ing results of four known yeast proteins. may now be feasible. (Rapid Commun. ples with the QqTOF. The mass resolution Each protein was found as the single Mass Spectrom. 1197,11,1015-24) match in the search. was >6000, and the mass accuracy was bet-
Re(DMPE)3+ detected in vivo The chemical form of radiopharmaceuticals is often unknown once they reach their target organs. For example, the imaging agent ["Tc(DMPE)J] (DMPE = l,2-bis(dimethylphosphino) ethane) is used in nuclear medicine to detect abnormalities in the heart, but the actual species that is responsible for creating the image is indeterminate. Methods for sensing in vivo reactions have traditionally relied on the use of microelectrodes such as carbon Scanning electron micrograph of the carbon fiber microelectrode tip. fibers, which have been used to detect neurotransmitters in the brains of laboratory animals. Wila modified carbon fiber microelectrode liam R. Heineman and co-workers at the sensor that determines the chemical University of Cincinnati have developed form of cationic electroactive comS0003-2700(97)09026-4 CCC: $14.00 © 1997 American Chemical Society
pounds in vivo. Because many radiopharmaceuticals are electroactive, this device has the potential to elucidate the chemical reactivity of such compounds after injection into test animals. The sensor was used to detect the chemical species [ReCDMPE)^], a nonradioactive analogue to the heart-imaging radiopharmaceutical [""Tc(DMPE)^, inside the beating heart of an anesthetized rat following injection. The microelectrode sensor consists of a 32-um carbon fiber, coated with Nation gel. The gel contains ion-exchange sites that preconcentrate cationic hydrophobic compounds. Oxidation of [Re(DMPE)^] to [Re (DMPE) §+] occurs at the sensor by scanning the potential from -200 to 400 mV. The microelectrode SPT1SOT* AV3.S also used to detect [Re(DMPE)J] in excised orceins and blood from rats injected with the compound It be possible to monitor the real time distribution of radiopharmaceuticals in vivo (I. Am Chew, Soc 1.97 119 6434-35)
Analytical Chemistry News & Features, September 1, 1997 5 1 9 A
