|Plant, David - UNIVERSITY OF MINNESOTA|
|Gengenbach, Burle - UNIVERSITY OF MINNESOTA|
Submitted to: National Plant Lipid Cooperative Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 8, 1997
Publication Date: N/A
Technical Abstract: Multi-subunit acetyl-coenzyme A carboxylase (ACCase) isolated from soybean chloroplasts is an unstable enzyme that loses activity following chloroplast lysis. We found that incubating the chloroplast stromal fraction under anaerobic conditions or in the presence of 5 mM FeSO4 stimulated both ACCase (acetyl-CoA to malonyl-CoA) and carboxyltransferase (malonyl-CoA to acetyl-CoA) activity. ACCase and carboxyltransferase activities were quantified by an HPLC analysis of product. Fe-activation was found to be associated with 59[Fe] binding to stromal protein. Total ACCase and carboxyltransferase activity measured in the stromal protein fraction containing bound 59[Fe] was 226% and 661% greater, respectively, than the control (stromal fraction not pretreated with FeSO4). Superose 6 gel filtration chromatography of the stromal protein fraction indicated that 59[Fe] bound to a stromal protein of approximately 178 kD that exhibited carboxyltransferase activity but lacked total ACCase activity. These results suggest that the multi-subunit ACCase of soybean chloroplasts is an iron containing enzyme, which may in part explain its labile nature.