THE C-TERMINAL OF RAT 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE IS INDISPENSABLE FOR ENZYME-ACTIVITY

We have cloned and overexpressed rat 4-hydroxyphenylpyruvate dioxygena se (4HPPD) in Escherichia coli. The soluble, active recombinant enzyme was shown to contain both 4HPPD and alpha-ketoisocaproate dioxygenase (alpha KICD) 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 alpha KICD activities, This finding suggests that the C-terminal extension domai n plays an essential role in the catalytic activity of the enzyme.