|Plank, David - UNIVERSITY OF MINNESOTA|
|Gengenbach, Burle - UNIVERSITY OF MINNESOTA|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: August 6, 1997
Publication Date: N/A
Technical Abstract: Acetyl-coenzyme A carboxylase (ACCase) is a biotinylated enzyme that catalyzes the MgATP-dependent carboxylation of acetyl-CoA to form malonyl- CoA. Dicot chloroplasts contain a multi-subunit ACCase that is known to be inherently unstable. We examined the effects of anaerobicity and metal ions on activity of the multi-subunit ACCase isolated from soybean chloroplasts. .Total ACCase activity was measured as the ATP-dependent conversion of acetyl-CoA to malonyl-CoA and the carboxyltransferase partial reaction was measured as the conversion of malonyl-CoA to acetyl-CoA in the presence of exogenous biotin. After 4 h of incubation at 4 C, total ACCase activity was increased 54% and 32% by the addition of 5 mM FeSO4 and maintaining anaerobic conditions during incubation, respectively. Carboxyltransferase activity, measured after 1 h of incubation, was stimulated 78% and 48% by the addition of 5 mM FeSO4 and anaerobic conditions, respectively. To determine whether the iron-induced stimulation of activity was due to protein binding of iron, the chloroplast stromal fraction was incubated in the presence of 59[Fe]SO4 for 1 h and then desalted on a G-25 Sephadex column. Stimulation of both total ACCase and carboxyltransferase activity by iron was associated with binding of 59Fe to stromal protein. Fractionation of the chloroplast stromal fraction on a Superose 6 column indicated that 59Fe bound to a single protein peak of approximately 70 kDa that exhibited carboxyltransferase activity but lacked total ACCase activity. These results suggest that the multi-subunit ACCase of soybean chloroplasts is an iron-containing protein which may in part explain its labile nature.