Ulen Gut Reaction

ULEN GUT REACTION (proposed by Ulen Gut in 1901), a method for biological differentiation of proteins through precipitation reaction, developed mainly by Ulen Gut and therefore named after him. U. r. is the only method that allows differentiation of proteins from various animal species, since this cannot be achieved chemically to this day. U. r. is used in forensic practice in the examination of bloodstains and others (see Precipitation), in the examination of certain food products when there is a question of whether meat, meat products, etc. belong to one or another animal species. When accounting for positive results with U. r., one must keep in mind the ability of specific precipitating sera to give a precipitate with the protein of related animals. In particular, it is impossible to differentiate between human and monkey blood, horse and donkey, sheep and goat, dog and fox. To distinguish proteins of related animals, Ulen Gut proposed the method of 'cross' immunization. To distinguish human blood from monkey blood, some Old World monkey, for example Macacus rhesus, is injected with human serum according to the rules for obtaining precipitating sera. The precipitating serum obtained in this way precipitates only human protein. The method of 'cross' immunization, however, is not applicable in all cases. Thus, it is impossible to obtain in horses serum that precipitates donkey protein. The method of 'cross' immunization has no effect in those related animals in which crossing is observed. To this day, it has not been possible to differentiate the blood of different human races either by precipitation reaction or by complement fixation reaction. Regarding the technique of U. r.-see Precipitation. The method of U. r. has some peculiarities in the examination of meat and other food products. In cases of suspicion of the presence of horse meat, U. r. is recommended to be performed as follows: with a previously calcined or boiled knife, a deep incision is made in the piece of meat to be examined. From the deep parts of the fresh incision, 30 g of meat without fat are taken. The taking of material and its crushing into small pieces is done on absolutely clean objects to avoid contamination with other protein. The crushed pieces of meat are placed in a sterile flask, to which 50 cm³ of sterile physiological solution is added. If canned meat (salted meat) is present, it must first be desalted. For this, sterile physiological solution or distilled water is added to the meat to be examined in the flask without shaking. The liquid is changed several times within 10 minutes, then the meat is left in 50 cm of sterile physiological solution for 3 hours at room temperature or overnight in an icebox. Shaking is not recommended, as this releases small droplets of fat present in the meat. Fat droplets float to the surface of the solution and cause undesirable cloudiness. Therefore, when fatty meat is present, it is necessary to add a few drops of chloroform to the solution. For orientation, whether there is sufficient protein concentration in the solution, 2 cm³ of the solution is taken into a test tube and shaken vigorously. The presence of persistent, non-disappearing foam indicates that there is sufficient protein in the solution. Then proceed to obtaining a pure filtered solution. The solution is filtered twice through filter paper previously moistened with physiological solution. The purity and clarity of U. r. depends on the concentration of proteins in the resulting meat solution. Take 1 cm³ of this solution, boil it in a test tube, and then add 1 drop of nitric acid solution (sp. gr. 1.153). The rapid precipitation of a flocculent precipitate indicates a high concentration of protein. Such a solution must be pre-diluted with sterile physiological solution. The degree of dilution is determined depending on the nature of the reaction with nitric acid. From the addition of a drop of nitric acid, a slight opalescence should appear in the solution and after 5 minutes a weak flocculent precipitate. The reaction of the solution is determined by litmus paper, it should be neutral or slightly alkaline (addition of 0.1% soda, avoid excess alkali that dissolves precipitins).-To set up U. r., take 6 test tubes. In the first and second, pipette 1 cm³ of the meat solution to be examined. In the third-1 cm³ of solution from horse meat (if we are talking about horse meat); in the 4th and 5th test tubes-1 cm³ each of pork and veal solution. In the 6th test tube-1 cm³ of sterile physiological solution from which the meat solutions were prepared. To all test tubes except the second, add 0.1 cm³ of transparent anti-horse precipitating serum. The addition of precipitating serum is done with a graduated pipette so that the serum slowly flows down the wall of the test tube and collects at the bottom. To the second test tube, add 0.1 cm³ of normal rabbit serum. The reaction is performed at room temperature, without shaking. After 20 minutes, the reaction should be complete. Later cloudiness is not evidence (see Precipitation). In positive cases, the reaction occurs in the 1st and 2nd test tubes, the remaining test tubes remain clear.-In cases of examination of sausages, it must be remembered that the meat is distributed unevenly, that it may be mixed with meat from other animals, so it is necessary to take larger quantities (50 g) for examination. The meat must be taken from different places. If there is a large amount of fat, the meat to be examined must be defatted before preparing the meat solution by exposing it to the action of ether or chloroform. Biological tests are also used to determine whether lard belongs to a given animal or not. U. r. is also used to distinguish natural honey from artificial honey.

3. Morgenstern.