High Protein Diets: Metabolic Poison for those with Inborn Errors of Amino Acid Metabolism - Essay Example

This defect is usually in an enzyme or transport protein, with a resultant block in the metabolic pathway. Subsequent toxic accumulations of substrates results in the disease. There are different forms of a metabolic disease and they vary in their mode of inheritance, onset and severity. This essay analyses normal amino acid chemistry and physiology, enzymes and enzyme defects in inborn errors of metabolism and specifically about some inborn errors of amino acid metabolism, namely phenylketonuria, homocystinuria and maple syrup disease.

Normal amino acid chemistry and physiology Amino acids (AA) are the fundamental building blocks of proteins and are small molecules with tetrahedral carbon covalently bound to an amino group, a carboxyl group, a variable (R) group and a hydrogen atom. There are 20 commonly occurring AA found in proteins and at least 150 other nonprotein amino acids. Normal turnover of amino acids occurs through a series of enzymatically controlled steps, the first of which is often a deamination or removal of the primary amine group to form the corresponding ?-ketoacid. These compounds are metabolized in a step-wise fashion, ultimately entering the tricarboxylic acid (TCA) cycle, leading to the formation of adenosine triphosphate (ATP).

Several AA are intermediaries in the urea cycle. AA are also found as intermediates in the transsulfuration pathway, as well as pathways involved in the generation and utilization of single carbon units. Normal levels of AA depend on a great extent on the age of the individual as well as nutritional status and overall health (McClatchey, 2002). Amino acids can be considered as three types: “the essential, nonessential, and conditionally essential. An essential or indispensable amino acid cannot be made by the body and must be supplied by food.

These include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.” Histidine is said to be a semi-essential amino acid since the body does not compulsorily need it. “Nonessential amino acids are made by the body from the essential amino acids or normal breakdown of proteins. The nonessential amino acids are arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, and tyrosine” (Peptide Guide, 2011.) Enzymes and enzyme defects in inborn errors of metabolism Genes exert their effects on organisms indirectly.

For most genes, the genetic information contained in the nucleotide sequence specifies a particular type of protein. Proteins control the chemical and physical processes of cells known as metabolism. Many proteins are enzymes, which are biological catalysts that accelerate biochemical reactions. Enzymes are essential for the breakdown of organic molecules, generating the chemical energy needed for cellular activities; they are also essential for the synthesis of small molecules and for their assembly into larger molecules and complex cellular structures (Hartl, 2009).

Any hereditary disease in which the cellular metabolism is abnormal results from an inherited defect in an enzyme. Such diseases are known as inborn errors of metabolism. Any sequence of biochemical reactions is called a biochemical pathway or a metabolic pathway. Each step requires a specific enzyme to catalyze the reaction and allow the chemical