Human digestive system
Chewing, in which food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which can be swallowed down the esophagus to enter the stomach. Here it is mixed with gastric acid until it passes into the duodenum where it is mixed with a number of enzymes produced by the pancreas. Saliva also contains a catalytic enzyme called amylase which starts to act on food in the mouth. Another digestive enzyme called lingual lipase is secreted by some of the lingual papillae on the tongue and also from serous glands in the main salivary glands. Digestion is helped by the chewing of food carried out by the muscles of mastication, by the teeth, and also by the contractions of peristalsis, and segmentation. Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion.
Adrian John Brown
He studied the rate of fermentation of sucrose by yeast and suggested in 1892 that a substance in the yeast might be responsible for speeding up the reaction. This was the first time enzymes were suggested as separate entities from organisms and talked about in chemical terms. He later studied the enzyme responsible and made the striking suggestion that the kinetics he observed were the result of an enzyme-substrate complex being formed during the reaction, a concept that has formed the basis of all later work on enzyme kinetics. Similar ideas had been put earlier by German chemist and Nobel laureate Hermann Emil Fischer by comparing substrate and enzyme with a key and a lock.