ENTEROKINASE — an enteropeptidaz (KF 184.108.40.206), the proteolytic enzyme of intestinal juice catalyzing transformation of trypsinogen in tripsinony E. belongs to peptide-hydrolases (see). Definition of activity E. in duodenal juice use at assessment of a functional condition of a mucous membrane of a small bowel, especially her upper part, and definition of activity E. in Calais — at assessment of a functional condition of a large intestine, its motility and microflora.
AA. it is opened by N. P. Shepovalni-kov in 1899 in I. P. Pavlov's laboratory. Generally this enzyme is produced by cells of a mucous membrane of a duodenum and upper part of a jejunum. Synthesis E. it is activated by trypsin (see) and ions of Na+. To an exit E. from cells of a mucous membrane in a gleam of a duodenum one of proteinaceous and peptide gastrointestinal hormones — secretin promotes (see).
AA. represents a glycoprotein, the molecule to-rogo consists not less than for 35% from carbohydrates; pier. the weight (weight) of enzyme is equal to about 150 Ltd companies. Molecule E. it is constructed of two polypeptide-nykh of chains — heavy (a pier. weight 115 000) and easy (pier. weight 35 000). These chains are connected among themselves by one or two disulfide (— S — S —) bonds. It is established that catalytic activity of enzyme is defined by a light chain. In structure of an active center E. the remains of serine enter (see) and a histidine (see), thus, enterokinase belongs to so-called serinovy proteinases (KF 3. 4.21).
In the course of transformation of trypsinogen into trypsin E. in a molecule of trypsinogen selectively hydrolyzes communication between the rest of a lysine in the 6th on a lozheniya and the rest from a leucine in the 7th situation and chips off thus N-trailer hexapeptide (Val-Asp-Asp-Asp-Asp-Lise) from a molecule of proferment. Change of conformation results (see) molecules of fermental protein and formation of an active center of trypsin. Speed of activation of trypsinogen under the influence of E. approximately by 2000 times active enzyme under the influence of trypsin exceeds the speed of its autocatalytic turning into.
AA. it is rather steady against effect of proteolytic enzymes; moving as a part of a digestive chyme, AA. activates trypsinogen in a gleam of a small bowel. In a large intestine under the influence of intestinal microflora E. it is inactivated.
Size of activity E. determine by Shlygin's method. Activation E is the basis for a method. crude drug of trypsinogen. Activation is carried out in reference conditions with use of a number of the increasing cultivations of the studied material (vodno! extracts from a calla or duodenal juice). In duodenal juice of the healthy person activity E., determined by this method, makes from 60 to 200 pieces/ml (sometimes to 300 pieces/ml), in Calais — from trace quantities to 20 pieces/g.
Activity E. in duodenal juice sharply increases after a resection of a stomach and decreases at damage of a mucous membrane of a duodenum. The squirrel leads the lowered consumption to decrease, and raised — to strengthening of synthesis and E. Aktivnost E. secretion in Calais at dysfunction of a large intestine increases to 200 pieces/g, and at the diarrhea accompanying acute intestinal diseases — to 2000 — 3000 pieces/g. Cases of genetically caused insufficiency E are described., clinically shown diarrhea, a neusvoyae-most of food and gipoproteinemiches-ky hypostases.
Bibliography: Definition of enterokinase as the test for assessment of a condition of intestines, sost. G. N. Shlygin, M., 1962; Peahens
I. P's fishing. Complete works, t. 2, book 2, page 15, M. — JI., 1951; Shepo-valnikov N. P. Physiology of intestinal juice, yew., SPb., 1899; L i e r-nieks J. J. a. Light A. The preparation and properties of bovine enteroki-nase, J. biol. Chem., v. 254, p. 1677, 1979; Maroux S., Baratti J. Des-nuelle P. Purification and specificity of porcine enterokinase, ibid., v. 246, p. 5031, 1971.
F. I. Komarov, B. F. Korovkin.