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Renin Angiotensin Mechanism.

Catabolism of phenylalanine and tyrosine and associated metabolic disorders.

 

Introduction:

  • The aromatic amino acids phenylalanine (Phe) and tyrosine (Tyr) have almost similar structure.

  • It is important to consume foods high in phenylalanine. 

  • Consuming tyrosine-rich foods, on the other hand, is not required. 

  • After being incorporated into proteins, phenylalanine has no other function than to convert to tyrosine. 

  • Tyrosine can thus reduce the body's need for phenylalanine. Tyrosine's sparing action on phenylalanine is known as the “sparing action.'

Catabolism of phenylalanine and tyrosine.

  • Both phenylalanine and tyrosine metabolism are interconnected and are degraded in the liver by the same pathway.

  • The p-hydroxyphenylpyruvate is produced by transamination of tyrosine. 

    • Enzyme: Tyrosine transaminase.

  • p hydroxyphenylpyruvate is decarboxylated and its phenyl ring is hydroxylated to form homogentisate. Ascorbic acid is needed for this reaction.

  • The benzene ring is removed by homogentisate oxidase, resulting in the formation of 4-Maleylacetoacetate. To break an aromatic ring, molecular oxygen is required.

  • Maleylacetoacetate is isomerized to 4-fumarylacetoacetate; 

    • Enzyme: maleylacetoacetate isomerase.

  • Fumarylacetoacetate is hydrolyzed to form Fumarate and acetoacetate. 

    • Enzyme: fumarylacetoacetate hydrolase.

  • Fumarate is an intermediate in the citric acid cycle and hence gluconeogenic.

  • Acetoacetate, which is a ketone body. 

  • Hence, tyrosine and phenylalanine are both ketogenic and glucogenic. 

Metabolic disorders:

  • Many metabolic disorders are associated with Catabolism of phenylalanine and tyrosine as,

    • Phenylketonuria, 

    • Albinism, 

    • Alkaptonuria,

    • Tyrosinemia.

  1. Phenylketonuria:

  • Phenylketonuria (PKU) is an hereditary metabolic disorder that results in a high level of phenylalanine in the blood.

  • The body can accumulate very high levels of phenylalanine which may prove toxic without treatment, resulting in mental retardation and other serious complications. 

  • Pregnant women who consume a lot of phenylalanine are more likely to have babies with mental retardation, heart problems, and small heads (microcephaly).

  • Their babies are exposed to phenylalanine before birth because it is found in their own blood in very high concentrations.

  1. Albinism:

  • Both parents carrying the albinism gene have a chance of passing the albinism gene to their child. 

  • The cause of albinism is a defect in one of several genes involved in producing and distributing melanin, the pigment responsible for skin, eyes, and hair coloration. 

  • Melanin may not be produced or may be produced in very small amounts due to the defect.

  • The gene for albinism is inherited from both parents, so a child must have both parents carry the gene. 

  • Parents who carry the albinism gene but don't have symptoms are typically carriers of the condition. 

  1. Alkaptonuria:

  • It's a very rare and hereditary disorder, which causes kidney problems. 

  • Caused due to lesser production or total lack of enzyme  homogentisic dioxygenase (HGD). 

  • Toxic substances such as homogentisic acid are broken down by this enzyme. 

  • Results in high levels of homogentisic acid.

  • Symptoms of Alkaptonuria:

  • There are dark spots on your eye's sclera (white)

  • The cartilage in your ears has thickened and darkened

  • Discoloration of your skin, especially in the sweat gland area, that is blue speckled

  • Sweat of a dark color or stains of sweat

  • Earwax that is black in color

  • A urinary stone and a prostate stone

  • Knee and hip arthritis (especially)

  • Heart problems can also occur as a result of alkaptonuria.

  1. Tyrosinemia:

  • The body lacks the enzyme [fumarylacetoacetate hydrolase (FAH). 

  • A person with tyrosinemia breaks down protein in their bodies in an abnormal way, allowing toxic breakdown products of tyrosine to build up in the body. 

  • There is progressive liver damage as well as kidney damage. 

  • It's a hereditary disorder.

Commonly Asked Questions.

  1. Discuss Catabolism of phenylalanine and tyrosine along with disorders associated with it.

  2. Write a short note on,

    1. Phenylketonuria, 

    2. Albinism, 

    3. Alkaptonuria,

    4. Tyrosinemia.
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