Phenylalanine control

Phenylketonuria was among the first inheritable metabolic defects discovered in humans. When this condition is recognized early in infancy, mental retardation can largely be prevented by rigid dietary control. The diet must supply only enough phenylalanine and tyrosine to meet the needs for protein synthesis. Consumption of protein-rich foods must be curtailed. Natural proteins, such as casein of milk, must first be hydrolyzed and much of the phenylalanine removed to provide an appropriate diet, at least through childhood. Because the artificial sweetener aspartame is a dipeptide of aspartate and the methyl ester of phenylalanine (see Fig. l-23b), foods sweetened with aspartame bear warnings addressed to individuals on phenylalanine-controlled diets. 

Amino acids are practical chiral educts (chirons), and they also steer stereoselective reactions as catalysts. Phenylalanine-controlled aldol condensations with 2-dialkyl-cyclopenta-l,3-dione give just one enantiomer (Danishefsky and Cain, 1976) Intramolecular cyclization reactions of serine yield chiral P-lactams via an active hydroxyl amide and after protection of the amino group of serine. The addition of aldehydes to cysteine produces chiral thiazolidinecarboxylic acids in quantitative yield. Aspartic and glutamic acids have been converted to... 

Many studies have focused on the blood phenylalanine level in treated PKU. Factors such as timing of treatment initiation, lifetime level of metabolic control, and current dietary status, all have an impact. In most studies, if treatment is initially delayed past the first 3 months of life, a child performs less well than siblings with PKU who are treated earlier. If metabolic control is variable throughout childhood, the individual tends to have poorer mental processing skills, slower reaction time, diminished achievement, and lower IQ scores. One study has documented IQ loss in early treated adolescents with elevated phenylalanine levels (Beasley et al., 1994). By 18 years of age, 27% have an IQ less than 70. IQ is significantly related to the average phenylalanine control between birth and 14 years of age. The current blood phenylalanine level in an individual with PKU is also correlated with reaction time (Clarke et al., 1987 Schmidt et al., 1994) and is... 

Hood A, et al. Variability in phenylalanine control predicts IQ and executive abilities in children with phenylketonuria. Mol Genet Metab. 2014 111(4) 445-51. 

Table 13.1 Outcomes in maternal PKU in relationship to timing of maternal blood phenylalanine control ...

The control solution (B) is used in this experiment to differentiate between the blue spots of glycine and phenylalanine. It will be seen that the Rp value of phenylalanine is greater than that of glycine. 

Phenylpyruvic acid can cause mental retardation m infants who are deficient m the enzymes necessary to convert l phenylalanine to l tyrosine This disorder is called phenylketonuria, or PKU disease PKU disease can be detected by a simple test rou tmely administered to newborns It cannot be cured but is controlled by restricting the dietary intake of l phenylalanine In practice this means avoiding foods such as meat that are rich m l phenylalanine... 

The mode of action is by inhibiting 5-enolpymvyl-shikimate-3-phosphate synthase. Roundup shuts down the production of the aromatic amino acids phenylalanine, tyrosine, and tryptophane (30). Whereas all these amino acids are essential to the survival of the plant, tryptophane is especially important because it is the progenitor for indole-3-acetic acid, or auxin, which plays an important role in growth and development, and controls cell extension and organogenesis. 

Biosynthesis of Tea Flavonoids. The pathways for the de novo biosynthesis of flavonoids in both soft and woody plants (Pigs. 3 and 4) have been generally elucidated and reviewed in detail (32,51). The regulation and control of these pathways in tea and the nature of the enzymes involved in synthesis in tea have not been studied exhaustively. The key enzymes thought to be involved in the biosynthesis of tea flavonoids are 5-dehydroshikimate reductase (52), phenylalanine ammonia lyase (53), and those associated with the shikimate/arogenate pathway (52). At least 13 enzymes catalyze the formation of plant flavonoids (Table 4). 

Methanol remains the most widely used modifier because it produces highly efficient separations, but it does not always produce the highest selectivity [8]. Recent studies have provided insight into the role of the modifier in enantioselectivity in SFC [69]. Blackwell and Stringham examined a series of phenylalanine analogues on a brush-type CSP and developed a model that allowed prediction of selectivity based on the bulk solvation parameters of various modifiers [70]. Careful choice of modifiers can be used to mask or enhance particular molecular interactions and ultimately provide control of selectivity [71]. 

Enantioselective enolate alkylation can be done using chiral auxiliaries. (See Section 2.6 of Part A to review the role of chiral auxiliaries in control of reaction stereochemistry.) The most frequently used are the A-acyloxazolidinones.89 The 4-isopropyl and 4-benzyl derivatives, which can be obtained from valine and phenylalanine, respectively, and the c -4-methyl-5-phenyl derivatives are readily available. Another useful auxiliary is the 4-phenyl derivative.90... 

Phenylalanine ammonia-lyase (PAL EC 4.3.1.5) is a pivotal enzyme in controlling flow of carbon from aromatic amino acids to secondary aromatic compounds (Figure 1) (28). PAL primarily deaminates phenylalanine to form t-cinnamic acid, however, in many species, it also less efficiently deaminates tyrosine to form -coumaric acid. Because PAL is restricted to plants and is an important enzyme in plant development, Jangaard (29) suggested that PAL inhibitors might make safe and effective herbicides, however, in his screen of several herbicides, he found no compound to have a specific effect on PAL. This was also the case in studies by Hoagland and Duke (30, 31.) in which 16 herbicides were screened. 

A qualitatively new approach to the surface pretreatment of solid electrodes is their chemical modification, which means a controlled attachment of suitable redox-active molecules to the electrode surface. The anchored surface molecules act as charge mediators between the elctrode and a substance in the electrolyte. A great effort in this respect was triggered in 1975 when Miller et al. attached the optically active methylester of phenylalanine by covalent bonding to a carbon electrode via the surface oxygen functionalities (cf. Fig. 5.27). Thus prepared, so-called chiral electrode showed stereospecific reduction of 4-acetylpyridine and ethylph-enylglyoxylate (but the product actually contained only a slight excess of one enantiomer). 

Akagi T, Kaneko T, Kida T et al (2005) Preparation and characterization of biodegradable nanoparticles based on poly(y-glutamic acid) with L-phenylalanine as a protein carrier. J Control Release 108 226-236... 

Flavonoids are the largest class of phenylpropanoids in plants. The basic flavonoid structure is two aromatic rings (one from phenylalanine and the other from the condensation of three malonic acids) linked by three carbons (Fig. 3.6). Chalcone is converted to naringenin by the enzyme chalcone isomerase, which is a key enzyme in flavonoid synthesis. This enzyme, like PAL and chalcone synthase (CHS), is under precise control and is inducible by both internal and external signals. Naringenin is the... 

Distortion of the plasma aminogram in individuals with an aminoaciduria also may lead to a relative failure of brain protein synthesis. Thus, in mice with a deficiency of phenylalanine hydroxylase, the blood concentration of phenylalanine is more than 20 times greater than the control value, leading to partial saturation of the transport system and a diminution in the brain level of neutral amino acids other than phenylalanine. Rates of protein synthesis were concomitantly reduced [8]. 

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