The quadrupole ion trap mass spectrometer--a small solution to a big challenge.

Innovations in ion trap mass spectrometry have exthose of standard amino acid derivatives. The technique requires a free amino terminus and a homogetended the applicability of this technique to the analysis of biological molecules. This tutorial review disneous sample. Typical sample quantities are at the 1to 10-pmol level (1). Posttranslational modifications to cusses basic ion trap theory and provides practical examples of how the theory is used to perform different amino acid residues cause anomalous retention times (2) and may be difficult to identify. Cycle times areC30 types of experiments such as molecular weight measurements, high resolution, and multiple stages of min/amino acid (1); thus; a peptide containing 25 amino acids would take 12.5 h to sequence. mass spectrometry (MS). Peptides generated from enzymatic digestion of a-casein, recombinant tissue plasBy contrast, mass spectrometry is a high-sensitivity, high-throughput technique used to acquire both molecminogen activator, and a cellular extract of proteins from Haemophilus influenzae illustrate the utility of ular weight and sequence information for proteins and peptides. Typical sample quantities are at the lowto ion trap mass spectrometers for the analysis of biochemical problems. mid-femtomole level (3). Time-of-flight instruments can be employed to obtain protein molecular weights Analysis of biochemical systems comprised of interacting proteins and peptides typically involves eluciwith two orders of magnitude improvement in mass accuracy over gel electrophoresis. Triple quadrupole dating the molecular weights of the biological molecules and obtaining their amino acid sequences. mass spectrometers are utilized to analyze enzymatic digests of proteins and tandem mass spectrometry can Covalent modifications to the primary sequence may affect protein function and must also be determined by be performed to elucidate amino acid sequence information for peptides through the use of collision-aided some means. Several complementary techniques are typically used to obtain this sort of information. Gel dissociation. The presence of posttranslational modifications is directly determined. Data may be generated electrophoresis provides an excellent visualization of the complexity of the biological process under study; in less than 1 min. Data interpretation has historically limited the throughput of the mass spectrometry aphowever, anomalies in migration afford poor mass accuracy and the presence of posttranslational modificaproach; however, a number of algorithms have been developed to automatically interpret tandem mass tions may be difficult to ascertain. Amino acid sequence information has historically been obtained using autospectra (4). Because of these advantages, mass spectrometry is mated Edman degradation. Chemical reagents are employed to remove one amino acid at a time from the developing into an essential technique for biochemical and biological research. The range of problems that amino terminus of an intact protein or peptide. The resulting amino acid derivative is purified and identimass spectrometry is currently being applied to includes the analysis of posttranslational modifications fication is obtained in a straightforward manner by of proteins (5); noncovalent protein–protein, protein– comparing the HPLC retention time of the sample to DNA, and protein–RNA interactions (6–9); study of peptides implicated in the functioning of the immune 1 Present address: National Jewish Center for Immunology and Respiratory Medicine, 1400 Jackson St., Denver, CO 80206. system (10–13); and the study of proteins involved in