p-Hydroxyphenylacetate-3-hydroxylase. A two-protein component enzyme

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• p-Hydroxyphenylacetate-3-hydroxylase is an inducible enzyme from Pseudomonas putida.
• It catalyzes the conversion of p-hydroxyphenylacetate to 3,4-dihydroxyphenylacetate.
• The enzyme comprises two components: a flavoprotein and a coupling protein.

Purpose of the Study:

• To elucidate the functional roles of the flavoprotein and coupling protein in p-hydroxyphenylacetate-3-hydroxylase activity.
• To develop a reliable assay for measuring the enzyme's product formation.
• To investigate the mechanism of enzyme catalysis and regulation.

Main Methods:

• Enzyme purification and characterization.
• Enzyme kinetic assays using p-hydroxyphenylacetate and substrate analogs.
• Development of a new assay utilizing homoprotocatechuate-2,3-dioxygenase.
• Spectroscopic analysis to identify redox centers.

Main Results:

• The flavoprotein alone exhibits wasteful NADH oxidase activity, producing H2O2.
• A 1:1 complex of flavoprotein and coupling protein is essential for stoichiometric product formation.
• Complex formation abolishes the flavoprotein's NADH oxidase activity.
• The coupling protein lacks a redox center, with FAD being the sole redox chromophore.

Conclusions:

• The coupling protein is crucial for the catalytic efficiency and specificity of p-hydroxyphenylacetate-3-hydroxylase.
• The enzyme functions as a two-component flavin hydroxylase, similar to other aromatic hydroxylases.
• Understanding this enzyme provides insights into microbial aromatic compound metabolism.