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General Features:
Abbreviated: Ile or I
Molecular formula: C6H13NO2
pKa: 2.36 (carboxyl), 9.60 (amino)
Physiological Roles:
Isoleucine's codons are AUU, AUC and AUA and is a non polar amino acid. It is classified as a hydrophobic amino acid because of the hydrocarbon side chain it possess. Its side chain is chiral (like threonine) meaning it has four possible stereoisomers, L-Isoleucine is the most common form and the form found most often in nature. As mentioned in the post on leucine, isoleucine is an isomer of leucine.
In eukaryotes Isoleucine is an essential amino acid, it cannot be synthesised. Foods that are high in this amino acid include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.
Isoleucine is a helpful amino acid in catabolic pathways. It can be converted to acetyl-CoA or acetoacetyl-CoA and from there be feed into the TCA cycle, It can also undergo transamination followed by oxidative decarboxylation and finally a series of oxidation reactions and be converted into propionyl-CoA. Porpionyl-CoA is a precursor for Succinyl-CoA, an essential component of the citric acid cycle (Nelson et al).
In Bacillus subtilis a gene named bkdR was found to control the utilization of isoleucine and valine as sole nitrogen sources (Debarbouille et al 1999).
Molecular formula: C6H13NO2
pKa: 2.36 (carboxyl), 9.60 (amino)
Physiological Roles:
Isoleucine's codons are AUU, AUC and AUA and is a non polar amino acid. It is classified as a hydrophobic amino acid because of the hydrocarbon side chain it possess. Its side chain is chiral (like threonine) meaning it has four possible stereoisomers, L-Isoleucine is the most common form and the form found most often in nature. As mentioned in the post on leucine, isoleucine is an isomer of leucine.
In eukaryotes Isoleucine is an essential amino acid, it cannot be synthesised. Foods that are high in this amino acid include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.
Isoleucine is a helpful amino acid in catabolic pathways. It can be converted to acetyl-CoA or acetoacetyl-CoA and from there be feed into the TCA cycle, It can also undergo transamination followed by oxidative decarboxylation and finally a series of oxidation reactions and be converted into propionyl-CoA. Porpionyl-CoA is a precursor for Succinyl-CoA, an essential component of the citric acid cycle (Nelson et al).
In Bacillus subtilis a gene named bkdR was found to control the utilization of isoleucine and valine as sole nitrogen sources (Debarbouille et al 1999).
When isoleucine is converted to an α-Keto acid it uses a branched chain α-keto acid dehydrogenase complex. When this enzyme is defective it results in a disease named maple syrup urine disease
There are five main steps in the synthesis of isoleucine.
Threonine dyhydratases catalyzes the first step in isoleucine biosynthesis. It will dehydrate threonine to create ammonia and 2-oxobutyrate. It is at this step that feedback inhibition by isoleucine itself will occur
Asetolactate synthase (Acetohydroxyacid synthase) is the next step and will catalyses the condensation of pyruvate and 2-oxobutyrate to yield acetohydroxybutyrate. Thiamine pyrophosphate (TPP) is a cofactor in this reaction used to stabilize pyruvate.
Acetohydroxyacid reductoisomerase will then reduce the acetohydroxybutyrate to produce 2,3-dihydroxy-3-methylvalerate.
From there dihydroxy-acid dehydratase will dehydrate the 2,3-dihydroxy-3-methylvalerate to form 2-oxo (keto)-3-methylvalerate
The final reaction is an aminotransferase from an amino acid donor to form isoleucine.
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