Dysfunctional enzymes can cause diseases

In 1934, the urine of two mentally retarded young siblings was found to contain phenylpyruvic acid, an unusual byproduct of the metabolism of the amino acid phenylalanine. It was not until two decades later, however, that the complex clinical phenotype of the disease that afflicted these children, called phenylketonuria (PKU), was traced back to its molecular phenotype. The disease resulted from an abnormality in a single enzyme, phenylalanine hydroxylase (Figure 17.1). This enzyme normally catalyzes the conversion of dietary phenylalanine to tyrosine, but it was not active in PKU patients' livers. Lack of this conversion led to excess pheny-lalanine in the blood and explained the accumulation of phenylpyruvic acid. Later, the amino acid sequences of phenylalanine hydroxylase in normal people were compared with those in individuals with PKU. In many cases, the only difference in the 451 amino acids that constitute this long polypeptide chain was that instead of arginine at position 408, many people with PKU had tryptophan.

Breakdown of proteins

Breakdown of proteins

Phenyl Pyruvic Acid Accumulation
Wq

2t Because conversion to tyrosine is blocked, phenylalanine and phenylpyruvic acid accumulate.

2t Because conversion to tyrosine is blocked, phenylalanine and phenylpyruvic acid accumulate.

Alkaptonuria

Tyrosine

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  • manuela hoffmann
    What cause disease of plasma membrane?
    8 years ago

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