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PKU Disease. Stephanie Inskeep Junior Biochemistry Major Spring 2009. Background. Inherited disease Lack of the enzyme phenylalanine hydroxylase (PAH) Catalyzes first step in the degradation of phenylalanine Phenylalanine transaminated to phenylpyruvate, a phenylketone compound

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pku disease

PKU Disease

Stephanie Inskeep

Junior Biochemistry Major

Spring 2009

background
Background
  • Inherited disease
  • Lack of the enzyme phenylalanine hydroxylase (PAH)
    • Catalyzes first step in the degradation of phenylalanine
  • Phenylalanine transaminated to phenylpyruvate, a phenylketone compound
  • Causes mental retardation if untreated
  • Babies have low phenylalanine diet until after maturation of brain
  • Chromosome 12, 451 amino acids in length
  • More the 60 different genes giving rise to nonfunctional PAH
slide4

A short time after administering a measured amount of phenylalanine to the subject, the concentration of phenylalanine in the blood plasma is measured. The level is usually substantially higher in people who carry one PKU gene (even though they show no signs of disease) than in individuals who are homozygous for the unmutated gene. Both parents must be heterozygous (must be carriers of the trait to produce a child with PKU disease (1 in 4 chance)

slide6

In the course of oxidizing phenylalanine to tyrosine, the enzyme PAH also oxidizes BH4 to BH2 (dihydrobiopterin).  The necessary BH4 must then be regenerated by the action of a separate enzyme, dihydropteridine reductase (DHPR).

questions
Questions…
  • Is phenylalanine glucogenic, ketogenic, or both? Why
  • Tyrosine is not an essential amino acid in normal people, but it is essential in persons with PKU. Explain why.
  • Patients with the disease PKU tend to have blue eyes, fair hair, and very light skin. Explain why.
  • Why is a PKU patient placed on a low phenylalanine diet instead of a phenylalanine free diet?
  • Draw the structure of aspartame (consists of a methylated Asp-Phe dipeptide) Would you let your patients take this product which is often found in artificial sweetener?
slide9

2.) Tyrosine involved in depression, eating, memory, sleep, it is even involved in which way you turn more – left or right) it’s pretty important to have. So people with PKU have to eat more food high in tyrosine to replace their lack of phenylalanine.

slide10

3.) The biochemical defect in albinism appears to be the absence of the enzyme tyrosinase, which prevents the synthesis of melanin pigment by pigment-forming cells. These individuals have a very white skin, fine white hair, pink or light blue irises of the eyes, and a variety of other eye disturbances