Courtesy: Human Genome Program, U.S. Department of Energy, Genomics and Its Impact on Science and Society: A 2008 Primer, 2008. (Original version 1992, revised 2001 and 2008.) http://genomicscience.energy.gov.
Improving Mass Spectrometry, Improving Biology
Beginning in the 1950s and continuing into the following decades, mass-spectrometry instrumentation advanced by leaps and bounds. With each improvement, both large and small, the number of biological researchers willing to employ mass spectrometry in their own labs increased. Mass spectrometry was on its way to becoming a staple technology of the petroleum industry, and chemists in that field were beginning to experiment on the instrumentation. As the decade progressed, the academic world became increasingly interested in mass spectrometry. Frank Field, who made the transition from mass spectrometry’s first big industry—petroleum—to biomedical research, noted: “Until you could look at proteins, big peptides, sugars, the biopolymers, you weren't in the forefront of or the mainstream of biomedical mass spectrometry” (42). Just as Biemann had initially experienced both excitement and frustration in his biological work with mass spectrometers, a growing number of researchers quickly realized any mass-spectrometric ability to push the frontier of research was expedited by better technology and better instrumentation. To push both mass spectrometry and biological research forward, researchers would need to shape the technology themselves.
Throughout the 1950s the biology community rapidly accepted the development of high-resolving-power mass spectrometers, which permitted the determination of accurate peaks throughout the mass spectrum and thus their elemental composition. This information was invaluable to the biology community, as it allowed for a closer look at many things: sequence determination of oligopeptides produced from the degradation of proteins, the tracing of metabolic transformations, structure determination in lipids, the structure and composition of alkaloids, and molecular-weight determination of antibiotics. But barriers remained and proteins were still beyond the reach of mass-spectrometry analysis.
At a 1998 talk, Henry Fales discusses his group's initial use of GC-MS. Courtesy of the ASMS Archives.
The first major technical developments bridging mass spectrometry and biology occurred in the late 1950s with developments in ionization techniques. The first methodology, field ionization/desorption, showed promise, but researchers found there were too many barriers for it be effective. Field and Burnaby Munson, chemists at Humble Oil, developed chemical ionization, which was adopted by a small group of biological researchers, including Hank Fales, who used a Marvin Vestal–built instrument to conduct studies on amino acids and other biochemical compounds. But it was the combination of mass spectrometry with gas chromatography—GC-MS—that stood as a turning point for mass spectrometry’s applicability in biological research. Gas chromatography separates a sample quickly and efficiently; and GC-MS, like chemical ionization, accommodated higher pressures of gas and other sample materials, thus allowing researchers the freedom to use the instrumentation for different types of biological materials. Klaus Biemann was among the first to use GC-MS in peptide and protein sequencing, for which he developed a strategy employing polyamino alcohol derivatives of peptides. Biemann wasn’t alone in using this method, as other, competing methods proliferated during the 1970s. Other researchers experimented with combining liquid chromatography with mass spectrometry (LC-MS) by various means. Many new techniques were attempted, but none was considered the definitive method for biological materials or the method that could be used for proteins. However, a few things were clear about this period from 1960 to 1980. The community was expanding, and a proliferation of ionization techniques demonstrated this growth. The new members of this community were joining seasoned pioneers in the continued chain of important contributions to the field.
Letter to Seymour Meyerson from Fulvio Cacace regarding the early pioneers of organic mass spectrometry, 1974. Seymour Meyerson Papers, CHF Collections. Click here for full size.
By 1980 instrumentation and biological research would be driven forward again—and brought to a much larger group of scientists—by Michael Barber and his colleagues, who introduced fast atom bombardment (FAB) ionization. FAB is a soft ionization technique in which a sample, in the condensed phase, is bombarded with high-energy particles, typically an inert gas. Chemists and the biology community were excited by FAB’s possibilities; it could analyze samples that were large and therefore not volatile enough to be analyzed by methods like electron impact or chemical ionization. Those samples included peptides, vitamins, nucleotides, hormones, monosaccharides, and steroids. FAB opened the door to mass-spectrometry analysis of larger nonvolatile compounds and jump-started the field of peptide mass spectrometry. Biemann recalls, “FAB-MS really opened up the field of peptide mass spectrometry to anybody who had a good mass spectrometer” (47). He noted that
the mass spectrometric peptide sequencing involved complex chemistry on a very small scale so it was not easily adapted by other laboratories. My laboratory was practically the only one that used that chemistry for mass spectrometry. All that changed when Mickey Barber invented fast atom bombardment ionization. (56)
One reason, Biemann recalled, for FAB’s popularity was that, unlike LC-MS and GC-MS, FAB worked “without any chemistry” and did not require a seasoned user. Instead, “with FAB, anybody could do it.” Simply put, the user of a FAB instrument did not have to be a seasoned chemist or a mass spectrometrist. A researcher could just use the instrument as a tool. Biologists were so eager to employ FAB that they did not wait for instrument manufacturers, instead buying requisite electronic units and having their university and industry machine shops modify existing equipment. FAB triggered a new wave of instrumentation innovation and new possibilities in sequence analysis of peptides. This work brought biologists closer to characterizing and sequencing proteins and to the field of proteomics, the study of the complete set of proteins in an organism, cell, or tissue, and how those proteins interact.