section_path: History and etymology/Discovery and early studies
section_name: Discovery and early studies
paragraph_text: Discovery and early studies
  
  Proteins have been studied and recognized since the 1700s by Antoine Fourcroy and others, who often collectively called them " albumins ", or "albuminous materials" (Eiweisskörper, in German). Gluten, for example, was first separated from wheat in published research around 1747, and later determined to exist in many plants. In 1789, Antoine Fourcroy recognized three distinct varieties of animal proteins: albumin, fibrin, and gelatin. Vegetable (plant) proteins studied in the late 1700s and early 1800s included gluten, plant albumin, gliadin, and legumin.
  
  Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the Swedish chemist Jöns Jacob Berzelius in 1838. Mulder carried out elemental analysis of common proteins and found that nearly all proteins had the same empirical formula, C H N O P S. He came to the erroneous conclusion that they might be composed of a single type of (very large) molecule. The term "protein" to describe these molecules was proposed by Mulder's associate Berzelius; protein is derived from the Greek word πρώτειος (proteios), meaning "primary", "in the lead", or "standing in front", + -in. Mulder went on to identify the products of protein degradation such as the amino acid leucine for which he found a (nearly correct) molecular weight of 131 Da.
  
  Early nutritional scientists such as the German Carl von Voit believed that protein was the most important nutrient for maintaining the structure of the body, because it was generally believed that "flesh makes flesh." Around 1862, Karl Heinrich Ritthausen isolated the amino acid glutamic acid. Thomas Burr Osborne compiled a detailed review of the vegetable proteins at the Connecticut Agricultural Experiment Station. Then, working with Lafayette Mendel and applying Liebig's law of the minimum, which states that growth is limited by the scarcest resource, to the feeding of laboratory rats, the nutritionally essential amino acids were established. The work was continued and communicated by William Cumming Rose.
  
  The difficulty in purifying proteins in large quantities made them very difficult for early protein biochemists to study. Hence, early studies focused on proteins that could be purified in large quantities, including those of blood, egg whites, and various toxins, as well as digestive and metabolic enzymes obtained from slaughterhouses. In the 1950s, the Armour Hot Dog Company purified 1 kg of pure bovine pancreatic ribonuclease A and made it freely available to scientists; this gesture helped ribonuclease A become a major target for biochemical study for the following decades.