Malic enzyme from archaebacterium Sulfolobus solfataricus. Purification, structure, and kinetic properties

Area of Science:

• Biochemistry
• Enzymology
• Extremophile Biology

Background:

• Malic enzymes are crucial in metabolic pathways, catalyzing the interconversion of malate and oxaloacetate.
• Thermoacidophilic archaea like Sulfolobus solfatararicus possess unique enzymes adapted to extreme environments.
• Understanding these enzymes provides insights into biological catalysis under harsh conditions.

Purpose of the Study:

• To purify and characterize the NADP-dependent malic enzyme from the thermoacidophilic archaea Sulfolobus solfatararicus.
• To investigate the enzyme's kinetic properties, stability, and cofactor requirements.
• To compare its characteristics with malic enzymes from other organisms.

Main Methods:

• Purification using ion exchange chromatography, ammonium sulfate fractionation, affinity chromatography, and gel filtration.
• Molecular weight determination via SDS-PAGE.
• Enzyme activity assays at varying temperatures, pH, and substrate concentrations.
• Determination of kinetic parameters (Michaelis constants, turnover number).

Main Results:

• Homogeneous purification of an NADP-preferring malic enzyme from S. solfatararicus.
• The enzyme is a dimer (Mr 105,000) with subunits of Mr 49,000.
• Optimal activity at 85°C and pH 8.0, requiring divalent metal cations.
• High thermostability and a turnover number of 376 s-1.
• Distinct kinetic properties and higher tryptophan content compared to E. coli malic enzyme.

Conclusions:

• The purified S. solfatararicus malic enzyme is a highly thermostable biocatalyst with unique properties.
• Its characteristics suggest potential applications in industrial processes requiring high temperatures.
• Further studies can elucidate its structural basis for thermostability and catalytic efficiency.