Arginine, named for silvery crystals, keeps cats alive and helps make nitric oxide
In 1886 a German chemist pulled a new amino acid from yellow lupin seedlings and named it after the Greek for silver, because its nitrate crystals gleamed white. Arginine turns out to matter hugely: a cat that misses it after a big meal can be poisoned by its own ammonia.
Ernst Schulze and his assistant Ernst Steiger isolated arginine in 1886, and Schulze worked out its structure with Ernst Winterstein in 1897, synthesising it two years later. Chemically it is a standard amino acid carrying an extra guanidino group, and at the body's pH it carries a positive charge. Only the L form occurs in nature, and its one-letter code, R, was picked because the letter sounds like the start of its name. Industry once extracted it by breaking down proteins such as gelatin; today fermentation of glucose yields 25 to 35 grams per litre.
Whether it counts as essential depends on who is eating. Most healthy adults make enough from glutamine by way of citrulline, and all protein foods contain it, from meat, milk and eggs to grains, beans and nuts. Premature babies cannot make it, however. Birds, which lack a urea cycle, must get it from food. Cats, dogs and ferrets break down protein so efficiently that a meal floods them with ammonia, which only the urea cycle can clear; without enough arginine the result can be fatal, though meat normally supplies plenty.
The body's production line is surprisingly spread out. Cells lining the small intestine make citrulline, the blood carries it to the kidneys, and kidney cells turn it into arginine and send it back, so damage to gut or kidneys can create a dietary need. Arginine is also a waypoint in the urea cycle, which converts toxic ammonia into urea for the urine, where urea holds about 90 per cent of the nitrogen. Mammals excrete nitrogen that way; fish release ammonium directly, and birds and reptiles use uric acid.
Arginine does many jobs: cell division, wound healing, immune function and hormone release, and T-cells need it to work properly. It is the raw material for nitric oxide, which helps regulate blood pressure. In proteins its charged head usually sits on the surface. Plants even route it toward alkaloids such as nicotine and cocaine, by way of a compound called putrescine.
Source: Arginine
