Arginine decarboxylase from a Pseudomonas species

Area of Science:

• Microbiology
• Enzymology

Background:

• Arginine decarboxylase (ADC) is a key enzyme in polyamine biosynthesis.
• Understanding ADC from different bacterial species provides insights into metabolic regulation and enzyme function.

Purpose of the Study:

• To isolate and characterize arginine decarboxylase from a Pseudomonas species.
• To compare the properties of this enzyme with known ADC enzymes from Escherichia coli.

Main Methods:

• Enzyme isolation and purification from Pseudomonas species.
• Enzyme activity assays at varying pH, substrate concentrations, and in the presence of cofactors and inhibitors.
• Characterization of kinetic parameters (Km) and inhibition constants (Ki).

Main Results:

• A constitutive arginine decarboxylase was purified approximately 40-fold.
• The enzyme showed properties similar to the biosynthetic ADC of E. coli.
• Optimal activity at pH 8.1, with absolute requirements for Mg2+ and pyridoxal phosphate.
• Inhibition by polyamines (putrescine, spermidine, cadaverine) and p-chloromercuribenzoate (PCMBS), with protection by dithiothreitol (DTT).
• Km for L-arginine was approximately 0.25 mM; D-arginine was a potent competitive inhibitor (Ki = 3.2 μM).

Conclusions:

• The characterized Pseudomonas ADC is a biosynthetic enzyme, distinct from inducible biodegradative enzymes.
• The enzyme's active site likely involves a sulfhydryl group.
• Polyamines and D-arginine can regulate ADC activity, impacting polyamine metabolism in Pseudomonas.