The C‐terminal of rat 4‐hydroxyphenylpyruvate dioxygenase is indispensable for enzyme activity

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Abstract
We have cloned and overexpressed rat 4‐hydroxyphenylpyruvate dioxygenase (4HPPD) in Escherichia coli. The soluble, active recombinant enzyme was shown to contain both 4HPPD and α‐ketoisocaproate dioxygenase (αKICD) activity. However, upon truncation of the 14 amino acids at the C‐terminus by site‐directed mutagenesis, the resulting mutant enzyme (rat F antigen) exhibited complete loss of 4HPPD and αKICD activities. This finding suggests that the C‐terminal extension domain plays an essential role in the catalytic activity of the enzyme.