1806

Amino Acids

Nicolas-Louis Vauquelin (1763–1829), Pierre-Jean Robiquet (1780–1840), Franz Hofmeister (1850–1922), Emil Hermann Fischer (1852–1919)

The term amino acid is familiar. If you ask people for a definition, most of them might say something about nutrition or bodybuilding, but those who mention proteins would be the winners. Amino acids all have a central carbon atom with an amine (NH₂) group on it, as well as a carboxylic acid (CO₂H) group. The simplest amino acid compound is glycine. If the compound has a methyl group coming off the central carbon, it is alanine, and if that methyl group has a benzene ring attached to it, it is phenylalanine. The differences between amino acids are all in the side chains attached to the core structure.

The French pharmacist Nicolas-Louis Vauquelin and his student, Pierre-Jean Robiquet, isolated the first known amino acid in 1806 and named it asparagine after the asparagus they used as a source. Almost a century later, German chemists Emil Hermann Fischer and Franz Hofmeister independently discovered that proteins were polymers of these building blocks, stringing them together in long chains, which then fold up into structures like the alpha-helix and beta-sheet. Protein synthesis is carried out by an extraordinary bit of cellular machinery called the ribosome, acting on instructions from the cell’s DNA sequence, in a process whose details are still generating Nobel prizes.

Joining two amino acids into a dipeptide requires a condensation reaction that results in the loss of a water molecule. The bond can then be broken by brute force or with the help of enzymes. If you’ve recently had anything to eat, your digestive system is dismantling proteins now. Digestive enzymes do this by holding them in just the right position and environment to be split, and thousands of other enzymes do the same for a wide variety of reactions in living cells. Our DNA codes for only twenty different amino acids, but that’s enough: even a short ten-peptide chain has over ten trillion possible combinations.

The asparagus plant is rich in asparagine, but it’s not the only source of this amino acid. Vauquelin and Robiquet could have used potatoes or licorice to make their discovery, but then it would surely have a different name.