Amino Acid Analyzer

Proteins are among the most diverse and important molecules in the natural world. They come in a variety of shapes and perform a variety of tasks, from speeding up chemical reactions in the body to forming the basic structures of skin and muscle. All proteins are made from long chains of smaller molecules known as amino acids. The order of the amino acids, along with the way the chains are folded into a three-dimensional structure, gives each protein its unique shape and chemical characteristics. In the molecular world, form is directly tied to function. Therefore, scientists hoping to study the role of a specific protein must first understand its structure.
Some of the earliest research on protein structure focused not on the complex three-dimensional shape, but on the most basic part of protein structure—the order of the amino acids in the protein chain, known as its primary structure. To begin to decipher this order, it is useful to calculate how many of each kind of amino acid are present in a protein molecule, a process known as amino acid analysis. In the 1940s and 1950s, scientists conducted amino acid analysis by hand using a technique called column chromatography. First, they obtained a sample of pure protein for analysis. Next, they destroyed the bonds between each amino acid link in the protein chain, resulting in a mixture of free amino acids. Each amino acid, while sharing a similar basic structure, has a section (known as a side chain) that makes it unique from the other amino acids.
In column chromatography, scientists use these unique properties to separate the different amino acids from one another. They add the amino acids from a protein to the top of a column containing a resin and a buffer solution of varying pH. Given that different amino acids react in different ways with the resin and the buffers, each kind of amino acid makes its way through the column in a unique amount time. With a constant rate of flow through the tube, chemists knew at what time each amino acid should emerge from the column. Using this standard, they could identify the presence of each amino acid in a sample.
As a sample left the column it mixed with ninhydrin and was heated, a reaction that turned the mixture blue. By analyzing the intensity of the blue color, scientists could determine the amount of a particular amino acid present in the sample. Together, these pieces of information formed the basis of an empirical formula for a protein.
The process for amino acid analysis described above was labor intensive. In the 1950s biochemists Stanford Moore (1913–1982), William Stein (1911–1980), and Darrel Spackman (born 1924) at Rockefeller University designed a machine to automate this complicated process. Working with the Rockefeller instrument shop, they built a device that automatically injected samples into columns, used timers to release buffers, and incorporated photometers attached to recording devices to analyze the intensity of the ninhydrin mixture.
Moore, Stein, and Spackman published the plans for their machine in a 1958 article in Analytical Chemistry. Although they never patented their invention, they did work closely with scientific instrument manufacturers to design a commercial model, which became available soon after 1958. Moore and Stein used their original machine, seen here, for many projects. Among these projects was research on ribonuclease, for which they won the 1972 Nobel Prize in Chemistry. Their machine remained in the lab space they had occupied at Rockefeller University through 1996. Researchers continued to use it long after Moore and Stein had retired. The photos of the object seen here show the amino acid analyzer installed at Rockefeller University just before it was disassembled and brought to the Smithsonian.
Moore-Stein Protein Sequencer Video Documentation, June 1996, Accession File 1997.3159, Archives Center, National Museum of American History.
Accession File 1996.0188, National Museum of American History.
William H. Stein and Stanford Moore, “The Chemical Structure of Proteins,” Scientific American 204, no. 2 (1961): 81-92.
Darrel H. Spackman, William H. Stein, and Stanford Moore, “Automatic Recording Apparatus for Use in the Chromatography of Amino Acids,” Analytical Chemistry 30, no. 7 (1958): 1190–1206.
Stanford Moore and William H. Stein, “Chromatographic Determination of Amino Acids by the Use of Automatic Recording Equipment,” Methods in Enzymology 6 (1963): 819–31.
Jeremy M. Berg, John L. Tymoczko, and Lubert Stryer, “3.2 Amino Acid Sequences Can Be Determined By Automated Edman Degradation” in Biochemistry (Macmillan, 2008): 102.
Stanford Moore and William H. Stein, “Chemical Structures of Pancreatic Ribonuclease and Deoxyribonuclease,” Science 180, no. 4085 (1973): 458–64.
Currently not on view
Object Name
amino acid analyzer
overall: 2 m x 61 m x 91.5 m; 6 9/16 ft x 200 1/8 ft x 300 3/16 ft
ID Number
catalog number
accession number
catalog number
Nobel Prize
Science & Scientific Instruments
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Medicine and Science: Chemistry
Science & Mathematics
Biotechnology and Genetics
Data Source
National Museum of American History, Kenneth E. Behring Center


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