PHENYLALANINE

From Big Medical Encyclopedia

PHENYLALANINE — a-amino-R-fe-nilpropionovaya acid, SBN5SN2 of CH(NH2)COOH, irreplaceable amino acid. T. it is necessary for ensuring normal life activity of the person, is molecular composition of all proteins (see) both of enzymes (see) animal and a plant origin, and also is a biosynthetic predecessor of tyrosine (see) and other nitrogen-containing connections. Genetically caused or secondary disturbances of exchange F. at the person lead to development of a serious illness.


Proteins contain 3 — 8% of phenylalanine. In a blood plasma of the person concentration F. makes 7 — 40 mg/l, daily excretion with urine of this amino acid reaches 150 — 30 mg.


T. takes part in formation of secondary structure (and - sleep - rali) proteins. In a molecule of hemoglobin (see) phenolic ring F. — unpolar (hydrophobic) amino acid — the subject, and replacement of the rest F provides hydrophobic contacts with flat structure. in situation 42 in a molecule of hemoglobin for the rest of other amino acid leads to disturbance of functions of hemoglobin and to heavy hemolitic anemia (see). Phenolic side chain of the rest F. in fermental proteins and proteinaceous substrates participates in hydrophobic interactions, providing thereby education enzyme - a substrate complex.

Pier. weight (weight) F. makes 165,2. The isoelectric point (see) is at pH 5,98. Absorption spectrum F. it is characterized by a maximum at 259 nanometers.

Phenylalanine exists in the form of L-and D-isomers (see the Isomerism) and a racemate (see. Racemic connections), and at live organisms there is only L-phenylalanine. Allocated from biol. objects L - fe-nilalanin represents leaflike crystals, bitterish on

taste. Specific rotation flat

20

st of the polarized light [a] equally — 34,4 ° (water); £ °pl 284 ° (with decomposition). In water solubility of L-phenylalanine at 16 ° makes 2,83 g / 100 ml, it is insoluble in alcohol and ether. D-phenylalanine also has an appearance of leaflike crystals; [afj is equal + 35 ° (water); / °pl 283 ° (with decomposition), water solubility at 25 ° 3 g / 100 the ml, in alcohol and ether is insoluble. Racemate F. represents colourless leaflike crystals, * °pl 271 ° (with decomposition) and 318 ° (with sublimation), water solubility at 25 ° is equal to 1,42 g / 100 to ml, in alcohol and ether we will dissolve badly, in benzene is insoluble.

Contents F. in biol. material determine x r about ma that r and fiches to them and (see the Chromatography), electrophoretic (see the Electrophoresis), enzymatic, microbiological and flyuorimetrichesky (see Flyuori-metriya) by methods.

In a human body and animals F. it is not synthesized therefore ensuring their normal life activity requires receipt F. with food. Daily requirement F. for the adult averages 31 mg/kg.

Multi-stage synthesis F. at plants it is carried out from eritrozo-4-phosphate and phosphopyruvate, to-rye deliver six carbon atoms for formation of an aromatic ring F., and also its side appreciate carbon atoms for creation.

At biosynthesis of proteins F. it is coded by a triplet of UUU — uracil-hurrah-tsil-uracil (see. Genetic code). In a liver F. is exposed to the irreversible hydroxylation leading to formation of tyrosine. Small part F. turns in predecessors of glucose (see) and ketone bodies (see). In an organism F. collapses to urea (see), carbonic acid (carbon dioxide) and water. Hydroxylation F. in tyrosine it is catalyzed by multicomponent system of phenyl of lanin-hydroxy-laznoy, in to-ruyu three enzymes enter: phenyl of a lanin-4-hydro-xymanhole (phenylalanine-4-monooksige-naza, KF 1.14.16.1), providing in the presence of other components of system and the 02nd direct hydroxylation of phenylalanine, i.e. formation of tyrosine, the diguide-ropteridinreduktaza (KF 1.6.99.7), a digidrofolatreduktaz (KF 1.5.1.3), and also tetrahydrobiopterine and NADF. Disturbance of synthesis or decrease of the activity fenilalanii-

4 hydroxylases leads to development in children of a classical form phenyl ketonuria (see), and decrease of the activity of dihydropteridinereductase, di-gidrofolatreduktazy or concentration of a tetrogidrobiopterin in blood is the reason of a giperfenilala-ninemiya, pathogenetic the leader to an oligophrenia (see) and to other psychoneurological frustration. Disturbance of normal functioning of any component of phenyl of lanin-gidroksilazny system causes in an organism accumulation F., exchange to-rogo begins to go on the way of education fenilgshrovino-gradny, phenyl-lactic, alpha-toluic to - t and other pathological derivatives F., allocated with urine. Pathology of exchange F. it is established not only at a hereditary giperfenilalaninemiya of different genesis, but also at diseases of a liver (see), to schizophrenia (see), rheumatism (see), alcoholism (see), psoriasis (see), anemias (see), diabetes (see a diabetes mellitus), a kwasiorkor (see), heart failure (see), a Down syndrome (see Down a disease), a viral hepatitis (see a viral hepatitis). See also Amino acids y.

Bibliography: Bochkov N. P. Genetics

of the person, page 218, M., 1978; M e c of l e r D. Biokhimiya, the lane with English, t. 1 — 3, M.,

1980; Whyte A. and d river. Fundamentals of biochemistry, the lane with English, t. 1 — 3, M., 1981.

A. M. Shaposhnikov.

Яндекс.Метрика