Amino Acid Metabolism Flashcards
Amino acids can be classified as
glucogenic & ketogenic
Amino acids whose catabolism yields
pyruvate
Amino acids whose catabolism yields pyruvate or one of the intermediates of the citric acid cycle are termed
glucogenic
Only exclusively found in proteins like leucine and lysine, which are not substrates for gluconeogenesis, preventing glucose formation.
Ketogenic amino acids
Asparagine hydrolyzed by
asparaginase
loses its amino group by transamination to form oxaloacetate.
Aspartate
can be administered systemically to treat leukemic patients, as it lowers asparagine levels in the plasma, depriving cancer cells of a required nutrient.
Asparaginase
This amino acid is converted to glutamate and ammonia by the enzyme glutaminase
Glutamine
Glutamine: This amino acid is converted to glutamate and ammonia by the enzyme?
glutaminase
Glutamate is converted to α-keto glutarate by transamination, or through oxidative deamination by?
glutamate dehydrogenase
This amino acid is oxidized to glutamate. Glutamate is transaminated or oxidatively deaminated to form α-ketoglutarate.
Proline
This amino acid is cleaved by arginase to produce ornithine
Arginine
This amino acid is oxidatively deaminated by histidase to urocanic acid, which subsequently forms N-formimino glutamate (FIGlu).
Histidine
Histidine: This amino acid is oxidatively deaminated by histidase to urocanic acid, which subsequently forms?
N-formimino glutamate (FIGlu)
Amino acids that form α-ketoglutarate via glutamate
- Glutamine
- Proline
- Arginine
- Histidine
Amino acids that form pyruvate;
- Alinine
- Serine
- Glycine
- Cystine
- Threonine
The major gluconeogenic amino acid. This amino acid loses its amino group by reversible transamination to form pyruvate.
Alanine
An amino acid can be converted to glycine and N^5, N^10 methylenetetra hydrofolate
Serine
Serine can be converted to glycine and N^5, N^10 methylenetetra hydrofolate. It can also be converted to pyruvate by?
serine dehydratase
This amino acid can be converted to serine by the reversible addition of a methylene group from N^5, N^10-methylenetetrahydrofolic acid or oxidized to CO2 and NH3.
Glycine
Glycine can be converted to?
glyoxylate
This amino acid is reduced to cysteine, using NADH + H^+ as a reductant.
Cystine
Cysteine undergoes desulfuration to yield?
pyruvate
This amino acid is converted to pyruvate or to α-ketobutyrate, which forms succinyl CoA.
Threonine
Amino acids that form fumarate:
- Phenylalanine and tyrosine
- Inherited deficiencies
Hydroxylation of phenylalanine produces?
tyrosine
in the enzymes of phenylalanine and tyrosine metabolism lead to the diseases phenylketonuria and alkaptonuria, and the condition of albinism.
Inherited deficiencies
Amino acids that form succinyl CoA:
methionine
is one of four amino acids that form succinyl CoA.
Methionine
This sulfur-containing amino acid deserves special attention because it is converted to S-adenosyl methionine (SAM), the major methyl-group donor in one-carbon metabolism.
Methionine
Methionine is also the source of?
homocysteine
a metabolite associated with atherosclerotic vascular disease.
homocysteine
a high-energy compound that is unusual in that it contains no phosphate.
SAM
is hydrolyzed to homocysteine and adenosine
SAH
accepts a methyl group from N5-methyltetrahydrofolate (N5-methyl-THF) requiring methylcobalamin.
Homocysteine
Homocysteine condenses with
serine
These amino acids are branched-chain amino acids that generate propionyl CoA, which is converted to succinyl CoA by biotin- and vitamin B12–requiring reactions
Valine and isoleucine
This amino acid is dehydrated to α-ketobutyrate, which is converted to propionyl CoA and then to succinyl CoA.
Threonine
Amino acids that form acetyl CoA or acetoacetyl CoA:
- Leucine
- Isoleucine
- Lysine
- Trytophan
This amino acid is exclusively ketogenic in its catabolism, forming acetyl CoA and acetoacetate.
Leucine
This amino acid is both ketogenic and glucogenic, because its metabolism yields acetyl CoA and propionyl CoA.
Isoleucine
An exclusively ketogenic amino acid, this amino acid is unusual in that neither of its amino groups undergoes transamination as the first step in catabolism.
Lysine
This amino acid is both glucogenic and ketogenic because its metabolism yields alanine and acetoacetyl CoA.
Tryptophan
Removal of the amino groups of all three amino acids is catalyzed by a single, vitamin B6–requiring enzyme, branched-chain amino acid aminotransferase.
Transamination
Removal of the carboxyl group of the α-keto acids derived from leucine, valine, and isoleucine is catalyzed by a single multienzyme complex, branched-chain α-keto acid dehydrogenase complex.
Oxidative decarboxylation
Oxidation of the products formed in the above reaction yields α-β-unsaturated acyl CoA derivatives.
Dehydrogenation
a carrier of one-carbon units
Folic acid
is produced from folate by dihydrofolate reductase in a two-step reaction requiring two NADPH.
tetrahydrofolic acid (THF)
allows one-carbon compounds to be recognized and manipulated by biosynthetic enzymes.
tetrahydrofolic acid (THF),
Most important disease of amino acid metabolism because it is relatively common and responds to dietary treatment. This is caused by a deficiency of phenylalanine hydroxylase. It is a common inborn amino acid metabolism error, characterized by phenylalanine accumulation and tyrosine deficiency.
Phenylketonuria (PKU)
may also caused by enzyme deficiencies required to synthesize BH4, or in dihydropteridine reductase, which regenerates BH4 from BH2.
Hyperphenylalaninemia
Characteristics of classic PKU:
- Elevated phenylalanine
- CNS symptoms
- Hypopigmentation
is present in elevated concentrations in tissues, plasma, and urine.
Phenylalanine
Mental retardation, failure to walk or talk, seizures, hyperactivity, tremor, microcephaly, and failure to grow are characteristic findings in
Phenylketonuria
The hydroxylation of tyrosine by tyrosinase, which is the first step in the formation of the pigment melanin, is competitively inhibited by the high levels of phenylalanine present in?
Phenylketonuria
is a treatable disease that requires early diagnosis due to its treatable nature
Phenylketonuria
is a family of diseases caused by over 100 mutations in the phenylalanine hydroxylase (PAH) gene, with frequency varying among populations and often doubly heterozygous
Classic PKU
is an essential amino acid and a key component of most natural proteins.
Phenylalanine
When a woman with PKU who is not on a low-phenylalanine diet becomes pregnant, the offspring will be affected with?
maternal PKU syndrome
is a rare autosomal recessive disorder characterized by a partial or complete deficiency in branched-chain α-keto acid dehydrogenase, an enzyme complex that decarboxylates amino acids.
Maple syrup urine disease (MSUD)
is a disorder with a classic type and several variant forms.
Maple syrup urine disease (MSUD)
- Defect in tyrosine metabolism leads to melanin production deficiency.
- Causes partial or full absence of pigment from skin, hair, and eyes.
Albinism
also known as tyrosinase-negative oculocutaneous albinism, results from copper-requiring tyrosinase deficiency.
Complete albinism
are inherited as autosomal recessive illnesses caused by a defect in the enzyme cystathionine β-synthase
Homocystinurias
• A Rare Metabolic Condition
• Deficiency in homogentisic acid oxidase leads to accumulation of homogeneic acid.
• Symptoms include homogentisic aciduria, large joint arthritis, and black ochronotic pigmentation of cartilage and collagenous tissue.
• Usually asymptomatic until age 40, with occasional diaper staining.
Alkaptonuria
