Tryptophan in horseradish peroxidase

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Horseradish peroxidase (HRP) is a crucial enzyme in various biochemical applications.
• Understanding the spatial relationship between enzyme active sites and key amino acid residues is vital for mechanistic studies.
• Fluorescent labeling offers a powerful tool for investigating enzyme structure-function dynamics.

Purpose of the Study:

• To develop fluorescent derivatives of horseradish peroxidase C (HRP C).
• To determine the distances between tryptophan residues and the porphyrin (heme) and substrate-binding sites.
• To assess the impact of modification on HRP C activity and substrate affinity.

Main Methods:

• Preparation of fluorescent HRP C derivatives by replacing protoheme with protoporphyrin or mesoporphyrin.
• Application of Förster energy transfer calculations to determine inter-residue distances.
• Chemical modification of the single tryptophan residue using 2-hydroxy-5-nitrobenzyl bromide (Koshland's reagent).

Main Results:

• Fluorescent HRP C derivatives were successfully synthesized.
• Distances were calculated: >2.2 nm between tryptophan and porphyrin, and >2 nm between tryptophan and the substrate-binding site.
• Enzyme activity towards hydrogen peroxide and ascorbate remained unaffected by tryptophan modification.
• Modified and unmodified HRP C exhibited identical affinities for aromatic substrates.

Conclusions:

• Fluorescent labeling of HRP C is achievable without compromising enzymatic function.
• The determined distances provide insights into the enzyme's structural organization.
• These fluorescent HRP C derivatives are suitable for further biochemical and biophysical investigations.