DESULPHONATION

From Big Medical Encyclopedia

DESULPHONATION — process of release of hydrogen sulfide or elemental sulfur of organic compounds; the amount of the sulfur removed from a human body can serve as additional diagnostic test at a number of diseases.

Big obshchebiol. D.'s processes serusoderzhashchy amino acids matter: cysteine (see), cystine (see), gomotsisteina and methionine (see), taking place in tissues of the person, animals, plants and at microorganisms with the participation of specific enzymes — desulfgidraz (KF 4.4), catalyzing not hydrolytic eliminating of hydrogen sulfide from a molecule of cysteine or a gomotsistein.

Earlier on the basis of the results received with the low-purified fermental extracts considered that formation of H 2 S from L-cysteine is catalyzed by specific enzyme — tsisteindesulfgidrazy. In recent years during the use of high cleaning drugs of enzymes it is established that process of release of H 2 S from L-cysteine is carried out by various fermental systems, namely gamma tsistationazoy, tsisteintransaminazy, serinsulfgidrazy, tsisteinliazy, the beta cyanoalaninesynthase of bean plants induced by a tryptophanase E. coli, etc. At action of each of these enzymes on cysteine H is formed 2 S while other part of a molecule of cysteine undergoes transformations as a result of which various products — pyruvate and ammonia (are formed at action of a tsistationaza and tryptophanase), glutamic acid (tsisteintransaminaza), serine, monothioesters of cysteine (serinsulfgidraza), lantionin, cysteic to - that (tsisteinliaza), tsianalanin (cyanoalaninesynthases). The main way of desulphonation of cysteine is connected with one of activities of multifunctional enzyme gamma tsistationazy which catalyzes also formation of cysteine from monothioester of a tsistationin and deaminizes homoserine. Earlier this reaction was attributed to a tsisteindesulfgidraza.

In the course of disintegration of cysteine an important role is played by vitamin B 6 . All enzymes participating in desulphonation of cysteine contain pyridoxal phosphate in quality of a coenzyme.

Formed in the course of. hydrogen sulfide (see) it is poisonous. In fabrics of an animal organism it quickly is exposed to enzymic oxidation to sulfates and is removed with urine in the form of thiosulphate, inorganic sulfate and efiroserny to - t. The sulfur of methionine which is formed as a result of its D. in an organism of animals is also oxidized to sulfates in preferential indirect way generally through D. of cysteine which is formed of methionine at its resulphonation.

In tissues of animals and microorganisms have also enzymatic anaerobic D.'s process L-cysteine, reacting interaminations with alpha ketoglutarate or pyruvate, turns into beta mercaptopyruvate. At action of a sulfuraza from beta mercaptopyruvate elemental sulfur (S) is chipped off and the pyruvate which is again reacting interaminations is formed. Due to excess of cysteine sulfur is recovered to H 2 S. Reaction proceeds according to the following scheme:

= At action of a sulfuraza from beta mercaptopyruvate is chipped off by alt elemental sulfur (S) and the pyruvate which is again reacting interaminations is formed. Due to excess of cysteine sulfur is recovered to H2S

Since the enzymes catalyzing biol., are pyridoxal phosphate - dependent, D.'s processes at animals and the person are broken at

V. Seurat's avitaminosis, released as a result of D., is brought out of a human body together with urine, edges contains inorganic sulfates, sulfates of indoxyl, phenol, cresol and organic (neutral) sulfur in invariable serusoderzhashchy amino acids.

Normal contains in daily urine of the person apprx. 3 g of sulfur. Its quantity increases at tuberculosis of intestines, peritonitises, intestinal stagnation, new growths, etc.

D.'s disturbance can lead to such diseases as gipermetioninemiya (see), homocystinuria (see), tsistationinuriya (see), Cystinuria (see), cystinosis (see).


Bibliography: Goryachenkova E. V. Enzymatic systems of biosynthesis and desulphonation of L-cysteine in an organism, Usp. biol, chemistry, under the editorship of B. N. Stepanenko, t. 10, page 64, M., 1969, bibliogr.; M of e i s-t e of of A. Biochemistry of the amino acids, v. 2, p. 757, N.Y. — L., 1965.

E.V.Goryachenkova.

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