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Look on the back of any can of diet soda and at the bottom of the list of ingredients you'll probably see the phrase 'Contains a source of phenylalanine'. This is because most sugar-free diet drinks utilise the artificial sweetener aspartame and aspartame contains the amino acid phenylalanine, which presents a major problem for those suffering from phenylketonuria (PKU). PKU is a serious genetic disorder characterised by an inability to metabolise phenylalanine, due to low levels of the enzyme phenylalanine hydroxylase. As a result, phenylalanine builds up in the blood and can flood the brain. In babies and young children, this flood of phenylalanine can be especially damaging, leading to the development of severe learning difficulties and seizures. But PKU is also one of the few genetic disorders that can be controlled by diet, with sufferers merely having to limit their intake of foods containing phenylalanine. Unfortunately, seeing as phenylalanine is not just found in diet drinks but also in protein-rich foods such as meat, fish, nuts and cheese, this is far from easy. With the help of nutritional supplements and warnings on food packaging, however, many sufferers are now successfully able to manage the disorder. In order to ward off any brain damage, this management process needs to start as soon as possible and so many countries regularly test newborn babies for PKU. This is done by measuring the level of phenylalanine in their blood; anything above 3mg/dL indicates potential problems. Furthermore, even though babies and young children are most at risk from PKU, sufferers need to control their intake of phenylalanine throughout their lives, which means regular blood tests. At the moment, one of the most accurate ways to measure levels of phenylalanine in the blood is high-performance liquid chromatography. But this requires chemically modifying the phenylalanine to ensure it can be clearly separated and detected. Perhaps high-performance anion-exchange chromatography (HPAEC) would make a superior alternative, postulated a team of South Korean researchers led by Seon-Pyo Hong at Kyung Hee University in Seoul. This follows their successful use of HPAEC in conjunction with pulsed amperometric detection (PAD), which detects biomolecules based on the current generated when they are oxidised at a special electrode, to measure levels of the sugar galactose in blood. Their aim was to diagnose those suffering from galactosemia; similar to PKU, this is a genetic disorder characterised by the inability to metabolise galactose. For galactose, Hong used an AEC column specifically designed to separate sugar molecules, known as Carbopac; whereas for phenylalanine he initially planned to use a column designed to separate amino acids, known as Aminopac. But when the researchers tested the two columns, both of which are produced by Dionex, Carbopac actually proved to be more effective at separating phenylalanine. This turned out to be because although Carbopac can retain phenylalanine it is unable to retain many other amino acids, allowing phenylalanine to be detected without too many interfering compounds. In addition, phenylalanine eluted much faster from the Carbopac column than the Aminopac column. This all meant that by using the Carbopac column with PAD, Hong and his team could accurately detect unmodified phenylalanine in complex mixtures of both amino acids and sugars in less than five minutes. Moving on to blood samples, they found that they could clearly detect and measure concentrations of phenylalanine down to levels under 1mg/dL, meaning the technique could readily be used to diagnose PKU sufferers. Related links:
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. |
 Diet sodas often contain phenylalanine. |
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