Related Experiment Videos
A multisubunit acetyl coenzyme A carboxylase from soybean
S Reverdatto1, V Beilinson, N C Nielsen
1United States Department of Agriculture, Agricultural Research Service, Purdue University, West Lafayette, Indiana 47907-1150, USA.
Plant Physiology
|March 9, 1999
Summary
Soybean acetyl-CoA carboxylase (ACCase) is a multisubunit enzyme essential for fatty acid biosynthesis. Researchers identified its components, determined their genetic origins, and demonstrated that the active enzyme can be reassembled from separate complexes, revealing insights into plant lipid metabolism.
Area of Science:
- Biochemistry
- Plant Molecular Biology
- Enzymology
Background:
- Acetyl-CoA carboxylase (ACCase) is a critical enzyme in fatty acid biosynthesis, catalyzing the rate-limiting step of malonyl-CoA formation from acetyl-CoA.
- Plastid ACCase is a multisubunit complex composed of biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and alpha- and beta-carboxyltransferase (CT) subunits.
Purpose of the Study:
- To characterize the multisubunit ACCase from soybean (Glycine max), focusing on the genetic origin and assembly of its components.
- To investigate the localization and integration of ACCase subunits within chloroplasts and their functional reconstitution.
Main Methods:
- Isolation and characterization of cDNAs encoding soybean ACCase subunits (BC, BCCP, alpha-CT, beta-CT).
- In vitro import and integration of translation products into isolated pea (Pisum sativum) chloroplasts.
- Edman microsequence analysis for identifying mature protein sequences.
- Generation of subunit-specific antibodies for tracking components during chloroplast fractionation.
- Size exclusion chromatography (Sephacryl 400) to analyze protein complexes and assess reassembly of enzymatic activity.
Main Results:
- Soybean ACCase comprises nuclear-encoded BC, BCCP, and alpha-CT, with the beta-CT subunit encoded by chloroplast DNA.
- Imported subunits integrated into functional ACCase within isolated chloroplasts, and their mature N-terminal sequences were identified.
- Two distinct high-molecular-mass complexes were isolated: one containing BC and BCCP (>800 kD), and another with alpha- and beta-CT (>600 kD).
- Mixing these complexes restored ACCase enzymatic activity, demonstrating the enzyme's capacity for reassembly, even between different plant species (soybean and pea).
Conclusions:
- The active form of soybean plastid ACCase can be reassembled from distinct protein complexes, highlighting a modular assembly process.
- This study provides crucial insights into the subunit composition, genetic regulation, and assembly mechanism of a key enzyme in plant fatty acid biosynthesis.