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At least 667 records · Page 37Linked to original sources
PubMed1968

Tyrosine transaminase: development of daily rhythm in liver of neonatal rat.

The development of the 24-hour rhythm in tyrosine transaminase activity was studied in the liver of the neonatal rat. A recognizable rhythm appears within 48 hours after birth, but it is opposite in phase to that observed in the adult rat. The reversal of the adult pattern occurs 21 to 23 days after birth and may represent a response to a change both in the eating pattern and in the amount of protein eaten.

Animals↗
PubMed1976

Purification and properties of chorismate mutase-prephenate dehydratase and prephenate dehydrogenase from Alcaligenes eutrophus.

Chorismate mutase and prephenate dehydratase from Alcaligenes autophus H16 were purified 470-fold with a yield of 24%. During the course of purification, including chromatography on diethylaminoethyl (DEAE)-cellulose, phenylalanine-substituted Sepharose, Sephadex G-200 and hydrogyapatite, both enzymes appeared in association. The ratio of their specific activities remained almost constant. The molecular weight of chorismate mutase-prephenast dehydratase varied from 144,000 to 187,000 due to the three different determination methods used. Treatment of electrophoretically homogeneous mutase-dehydratase with sodium dodecyl sulfate dissociated the enzyme into a single component of molecular weight 47,000, indicating a tetramer of identical subunits. The isoelectric point of the bifunctional enzyme was 5.8. Prephenate dehydrogenase was not associated with other enzyme activities; it was separated from mutasedehydratase by DEAE-cellulose chromatgraphy. Chromatography on DEAE Sephadex, Sephadex G-200, and hydroxyapatite resulted in a 740-fold purification with a yield of 10%. The molecular weight of the enzyme was 55,000 as determined by sucrose gradient centrifugation and 65,000 as determined by gel filtration or electrophoresis. Its isoelectric point was pH 6.6. In the overall conversion of chorismate to phenylpyruvate, free prephenate was formed which accumulated in the reaction mixture. The dissociation of prephenate allowed prephenate dehydrogenase to compete with prephenate dehydratase for the substrate.

Alcaligenes↗
PubMed1992

Biosynthetic precursors of deazaflavins.

The incorporation of 13C- and 14C-labeled precursors into 5-deaza-7,8-didemethyl-8-hydroxyriboflavin (factor F0) was studied with growing cells of Methanobacterium thermoautotrophicum. 5-Amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione was incorporated into the deazaflavin and into riboflavin without dilution. Tyrosine and 4-hydroxyphenylpyruvate were incorporated into the deazaflavin and into cellular protein. 4-Hydroxybenzaldehyde was not incorporated. A reaction mechanism is proposed for the formation of the deazaflavin chromophore from 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione and tyrosine or 4-hydroxyphenylpyruvate.

Flavins↗
PubMed1971

Phenylketonuria.

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Child↗
PubMed1976

Behavioral and biochemical correlates of diet change in phenylketonuria.

The investigation was designed to explore the use of tests tapping reversible aspects of behavior and performance and to find out whether these data can be correlated with concurrent metabolic changes in different dietary phases. The four subjects had classic phenylketonuria, diagnosed on the basis of a high level of serum phenylalanine on a regular diet, and severe mental retardation. Three types of diet were used: the general institutional diet, a low phenylalanine diet, and a low phenylalanine diet with added L-phenylalanine. A position discrimination and reversal task was used. Blood samples were taken every week on the day before psychological testing, and one 24-hr urine sample was collected during each dietary phase. In subjects I and II performance deteriorated upon elevation of the serum phenylalanine level, but these changes were transient only, thus showing an adaptation to the effects of the high serum phenylalanine level. Subject III showed increased response latencies (slower test responses) during high phenylalanine diet phases and faster responses while on a low phenylalanine diet. The correlation between response time and phenylalanine level is highly significant (r = 0.86, P less than 0.001). On the low phenylalanine diet subject IV's responses were fast and her performance was very stable, which contrasted with erratic performance during the high phenylalanine phases. Calculations show a significant association with phenylalanine level, both for response time (r = 0.47, P less than 0.05) and for variability in response time within each session (r = 0.46, P less than 0.05). Biochemical variability was observed in metabolic responses to phenylalanine loading, especially in the excretion of tryptophan metabolites.

Adolescent↗
PubMed1983

The X-ray crystal structure analysis of the refined complex formed by bovine trypsin and p-amidinophenylpyruvate at 1.4 A resolution.

The X-ray crystal structure of the complex formed by bovine beta-trypsin and the potent small inhibitor p-amidinophenylpyruvate at pH 7.6, has been determined by difference Fourier methods at 1.4 A resolution and subsequently refined to a crystallographic R value of 0.191, applying diagonal matrix least-squares procedures including energy constraints. The amidino and the phenyl group of this inhibitor are bound to the specificity pocket, essentially as previously observed in benzamidine-trypsin. The reactive Ser195 O gamma of trypsin forms a covalent bond of length 1.7 A to the carbonyl carbon of the pyruvate group. The hybridization of this carbonyl carbon is just between trigonal and tetrahedral. The imidazole ring of His57 is in a correct orientation to form bonds via its N epsilon 2 hydrogen to one of the carboxylate oxygens of p-amidinophenylpyruvate and to Ser195 O gamma. The probable proton shift makes Ser195 O gamma more nucleophilic and the attacked carbonyl carbon of p-amidinophenylpyruvate more electrophilic and thus facilitates bond formation. These specific interactions offer a qualitative explanation for the unique binding properties of p-amidinophenylpyruvate and for the applicability of the quantitative structure-activity relations previously found by Markwardt and coworkers for three series of p-amidinophenylalkanone compounds with carbonyl groups in alpha-, beta- and gamma-position to the phenyl ring.

Animals↗
PubMed1985

Transition-state inhibition of thrombin and trypsin by amidinophenylpyruvates.

The interactions of human thrombin and bovine trypsin with 4-amidinophenylpyruvate (p-APPA), 3-amidinophenylpyruvate (m-APPA) and benzamidine were studied by equilibrium binding and by stopped-flow kinetics with proflavin displacement. The excellent inhibitory properties of p-APPA with both enzymes are explained by a two-step transition-state mechanism in which the initial Michaelis complex E.I reacts rapidly to form a fairly stable, chemically bonded complex E-I, in which the keto group of p-APPA forms a hemiketal with the gamma-O-atom of Ser195 at the active site. The hemiketal complex of thrombin and p-APPA may be further stabilized by a hydrogen bond between a carboxylate oxygen of p-APPA and the N tau-atom (= N epsilon 2) of His57, as was previously shown for the trypsin-p-APPA complex by X-ray crystal structure analysis by J. Walter and W. Bode. m-APPA is apparently sterically incapable of forming a hemiketal with Ser195 O gamma; it does not bind to thrombin or trypsin in a time-dependent manner, and it displays KI values with both enzymes close to those obtained for benzamidine itself. In the p-APPA-thrombin reaction the overall binding constant KI (E-I) is 1.3 microM, while the initial binding displays a KM (E.I) estimated at least 100-fold higher (700 microM). The half-time for the formation of E-I is about 0.6 s at a p-APPA concentration of 1 microM.

Animals↗