Health & Medical Nutrition

Essential Amino Acid: Phenylalanine & Valine

Phenylalanine: The phenylalanine is an essential amino acid. It is not synthesized in the body but in the micro-organism it is synthesized where one molecule of D-erythrose-4 phosphate and two molecules of phosphot-enolpyruvic acid are required. Metabolic breakdown of phenylalanine lead to formation of tyrosine, phenyl acetic acid, phenyl lactic acid, and tissue protein in separate reactions.

The phenylalanine gets first converted to tyrosine by phenylalanine hydroxylase. One of the major hereditary metabolic disorder called phenylketonuria impairs this conversion is hyperpheylalaninemia i.e. mental retardation. This is due to absence of the enzyme phenylalanine oxidase responsible for this conversion, causing defective mental development in children and a high plasma phenylalanine and its increased excretion in urine.

The symptoms like seizures, eczema, and psychosis can be avoided by prompt treatment. Administration of phenylalanine in such cases would result in prolonged elevation of this amino acid in the blood, indicating diminished tolerance to phenylalanine.

It is effective in weight control due to increased thyroid secretion and reduced appetite. It keeps kidneys and bladder efficient. Its deficiency results in reduce in eyes, and behavioral changes.

It is available in plenty in Italian millet, varagu, horse gram, red gram, bengal gram, fenugreek, spinach, colocasia, potato, radish, yam, bitter gourd, brinjal, jack, almond, gingelly seed, ground nut, piyal seeds, banana, egg, milk, curd, cheese, and persimmon. The RDA for children is 22 mg, and for adults is 14 mg per kg. of body weight including that for tyrosine.

Valine: It is an aminoisovaleric acid. It is essential and not synthesized in the body. It is synthesized in the micro-organism from the pyruvic acid. Pyruvic acid is decarboxylated with the formation of acetaldehyde which condenses with another molecule of pyruvic acid to form acetolactic acid. Thiamine pyrophosphate is required for such process of condensation.

An inherited defect of the decarboxylase step results in accumulation of the amino acid in blood, urine, and CSF, though the incidence is only 1:2500000. In the classic type, affected infants appear normal at birth but develop frequent vomiting and failure to thrive. Acute ketoacidotic episodes, often triggered by recurring infections, result from increased production of organic keto acids.

Severe neurological dysfunction leads to seizures, coma, respiratory failure, and death in many patients. Survivors are usually mentally retarded. Milder variants of the disease, identified by enzyme analysis of leukocytes or fibroblasts are known. The catabolism of valine leads to succinyl-CoA and CO2. It is needed for the proper performance of the nervous and digestive system.

Sources of Phenylalanine: It is found in plenty in ragi, paraboiled rice, varagu, horse gram, rajmah, agathi, safflower leaves, radish, colocasia, bitter gourd, jack, piyal seeds, pistachio, peaches, avocado, egg, and cheese. The RDA for children is 25 mg, and for adults is 10 mg per kg. of body weight.

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