Purification and properties of thiamine pyrophosphokinase in Paracoccus denitrificans

Area of Science:

• Biochemistry
• Enzymology
• Microbial Physiology

Background:

• Thiamine pyrophosphokinase (TPK) activity was first identified in procaryotic cells of Paracoccus denitrificans.
• The enzyme's role in thiamine metabolism and its molecular characteristics in procaryotes were previously uncharacterized.

Purpose of the Study:

• To purify thiamine pyrophosphokinase from P. denitrificans.
• To elucidate the molecular structure and biochemical properties of the purified enzyme.

Main Methods:

• Enzyme purification using chromatography techniques (620-fold purification).
• Molecular weight determination via SDS-polyacrylamide gel electrophoresis, gel filtration (Sephadex G-150), and sedimentation equilibrium analysis.
• Enzyme kinetics and inhibition studies using varying substrate (thiamine, ATP) and inhibitor (pyrithiamine, oxythiamine, chloroethylthiamine) concentrations.

Main Results:

• Purified TPK exhibited a molecular weight of 23,000 Da on SDS-PAGE, suggesting a dimer with a native molecular weight of 44,000 Da.
• Sedimentation equilibrium indicated a higher molecular weight (96,000 Da), likely representing an aggregated form of the functional dimer.
• The enzyme required thiamine, ATP, and Mg2+, with Km values of 10 µM for thiamine and 0.38 mM for ATP.
• Competitive inhibition by pyrithiamine (Ki = 19 µM) and product inhibition by TPP were observed.

Conclusions:

• The study successfully purified and characterized thiamine pyrophosphokinase from P. denitrificans.
• The enzyme exists as a dimer and catalyzes the pyrophosphorylation of thiamine, with specific kinetic properties and inhibition patterns identified.