Why ancient farmers paired beans with maize: the missing amino acid lysine
Maize is short on lysine, one of the amino acids the human body cannot make for itself. Beans are rich in it. So it may be no accident that the archaeological record so often finds the two crops together, most famously in the Three Sisters planting of beans, maize and squash.
Lysine is one of the building blocks of proteins, and because humans lack the machinery to build it, every bit must come from food. It is the limiting amino acid in most cereal grains, the essential one present in the smallest amount, while pulses such as beans and peas have plenty. Eggs, meat, soy, Parmesan cheese and fish such as cod and sardines are also rich sources. Nutritionists count a food's protein as adequate in lysine when it contains at least 51 milligrams per gram, or 5.1 percent.
Organisms that can make it use one of two routes. Bacteria and plants follow the diaminopimelate pathway, which starts from the amino acid aspartate, while yeasts, higher fungi and some protists use the alpha-aminoadipate pathway, built from different ingredients. Breeders have long hoped to engineer cereals richer in lysine by jamming the plant's feedback controls, but success has been limited, probably because excess free lysine is toxic to the plant.
In the body, lysine does far more than slot into proteins. It helps crosslink the collagen that gives connective tissue its strength, aids the absorption of essential minerals, and feeds the production of carnitine, a molecule central to burning fatty acids. Chemical tags on lysine in histones, the spools DNA wraps around, help control which genes are active. Too little can lead to weak connective tissue and anaemia; too much, when the body fails to break it down, can cause severe neurological disorders.
Ferdinand Drechsel first isolated it in 1889 from casein, the milk protein, naming it from the Greek lysis, loosening. Emil Fischer and Fritz Weigert worked out its structure in 1902. Its odd one-letter code, K, arose because L was already taken by the simpler leucine and M by methionine.
Source: Lysine
