Enzyme Structure
HPPD is an enzyme that usually bonds to form tetramers in bacteria and dimers in eukaryotes and has a subunit mass of 40-50 kDa. Dividing the enzyme into the N-terminus and C-terminus one will notice that the N-terminus varies in composition while the C-terminus remains relatively constant (the C-terminus in plants does differ slightly from the C-terminus in other beings). In 1999 the first X-ray crystallography structure of HPPD was created and since then it has been discovered that the active site of HPPD is composed entirely of residues near the C-terminus of the enzyme. The active site of HPPD is has not been completely mapped, but it is known that the site consists of an iron ion surrounded by amino acids extending inward from beta sheets (with the exception of the C-terminal helix). While even less is known about the function of the N-terminus of the enzyme, scientists have discovered that a single amino acid change in the N-terminal region can cause the disease known as hawkinsinuria.
Read more about this topic: 4-Hydroxyphenylpyruvate Dioxygenase
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