Spinach leaf acetyl-coenzyme a synthetase: purification and characterization.

Area of Science:

• Plant Biochemistry
• Enzymology
• Molecular Biology

Background:

• Acetyl-coenzyme A (CoA) synthetase plays a key role in cellular metabolism.
• Understanding its function in plants is essential for elucidating fatty acid synthesis pathways.

Purpose of the Study:

• To purify and characterize acetyl-coenzyme A (CoA) synthetase from spinach leaves.
• To investigate the enzyme's kinetic properties and substrate specificity.
• To assess the enzyme's role in providing acetyl-CoA for chloroplast functions.

Main Methods:

• Enzyme purification using ammonium sulfate fractionation, ion exchange, dye-ligand, and gel permeation chromatography.
• Determination of kinetic parameters (Michaelis constants, K(i)) for substrates.
• Assessment of substrate specificity and inhibition by potential effectors.

Main Results:

• Acetyl-coenzyme A (CoA) synthetase was purified 364-fold from spinach leaves.
• The enzyme exhibited specific activity of 2.77 units/mg protein with a native M(r) of approximately 73,000.
• Michaelis constants were determined for Mg-ATP (150 µM), acetate (57 µM), and CoA (5 µM), with substrate inhibition by CoA observed.

Conclusions:

• The purified spinach acetyl-coenzyme A (CoA) synthetase is specific for acetate.
• Its kinetic properties support its role as a primary source of chloroplast acetyl-CoA.
• The enzyme is not significantly inhibited by fatty acid synthesis intermediates or products in vitro.