Geranylgeranyl pyrophosphate synthetase lacking geranyl-transferring activity from Micrococcus luteus

Area of Science:

• Enzymology
• Biochemistry
• Microbiology

Background:

• Geranyl pyrophosphate synthetase (GPPS) is crucial for isoprenoid biosynthesis.
• Understanding GPPS in microorganisms like Micrococcus luteus provides insights into metabolic pathways.

Purpose of the Study:

• To purify and characterize geranyl pyrophosphate synthetase from Micrococcus luteus.
• To investigate the enzyme's catalytic activities and substrate specificities.
• To explore the potential for dual catalytic functions within the purified enzyme fraction.

Main Methods:

• Multi-step protein purification using DEAE-Sephadex, hydroxylapatite, and Sephadex G-100 chromatography.
• Enzyme activity assays to determine kinetic parameters (Km) and optimal conditions (pH, Mg2+).
• Molecular weight estimation via Sephadex gel filtration.
• Inhibition studies using specific reagents like iodoacetamide and Triton X-100.

Main Results:

• GPPS was purified 490-fold with a pH optimum of 7.7 and estimated molecular weight of 70,000 Da.
• Km values for isopentenyl pyrophosphate and dimethylallyl pyrophosphate were determined as 8 µM and 62 µM, respectively.
• The enzyme required Mg2+ and was stimulated by Tween 80, inhibited by Triton X-100, inorganic pyrophosphate, and iodoacetamide.
• The purified fraction catalyzed both geranyl pyrophosphate and geranylgeranyl pyrophosphate synthesis, suggesting potential dual activity or a mixture of enzymes.

Conclusions:

• The study demonstrates the successful purification and characterization of a GPPS from M. luteus.
• Evidence suggests the enzyme fraction possesses geranylgeranyl pyrophosphate synthetase activity, distinct from previously known enzymes.
• The findings indicate either a single enzyme with dual catalytic sites or a mixture of GPPS and geranylgeranyl pyrophosphate synthetase.