Characterization of Maize Acetyl-Coenzyme A Carboxylase

Abstract

Maize (Zea mays L.) leaf acetyl-COA carboxylase (ACCase) was purified about 500-fold by ammonium sulfate fractionation and gel filtration and blue Sepharose affinity and anion-exchange chromatography. Most ACCase activity (85%) recovered from the anion-exchange column was found in a highly purified fraction (specific activity 5.5 bmol acid-stable product min-' me-') that consisted primarily of a single 227-kD biotinylated polypeptide. The fraction represented 29% of the original activity and was designated ACCase 1. A second partially purified ACCase activity (ACCase II) eluted earlier during anion-exchange chromatography, contained a single biotinylated polypeptide of 219 kD, was poorly recognized by antiserum raised against the ACCase I polypeptide, and was less inhibited by the herbicides haloxyfop or sethoxydim than was ACCase 1. ACCase I and II both utilized propionyl-COA as substrate about 50% as effectively as acetyl-COA, and neither utilized methylcrotonyl-COA. lmmunoprecipitation with antiserum and protein blotting of crude extracts of leaf, embryo, and endosperm tissue and suspension cells indicated that most ACCase activity in these tissues was immunologically similar and consisted of ACCase 1. Only leaves contained significant amounts of the ACCase II polypeptide; however, no ACCase II polypeptide was found in isolated mesophyll chloroplasts. The ACCase I and II polypeptides appear to be subunits of distinct ACCase isoforms.

Lipid biosynthesis.

“…However, the Gramineae family of plants is different in that both the plastid and cytosolic ACCase isozymes are large multifunctional polypeptides (Egli et al, 1993;Konishi and Sasaki, 1994). Coincident with this evolutionary difference, the chloroplast genomes of rice and maize have lost the gene that encodes the putative carboxyltransferase subunit of the prokaryotic-type ACCase.…”

An Isoleucine Residue within the Carboxyl-Transferase Domain of Multidomain Acetyl-Coenzyme A Carboxylase Is a Major Determinant of Sensitivity to Aryloxyphenoxypropionate But Not to Cyclohexanedione Inhibitors

“…These chemicals inhibit the CT activity, thus blocking the transfer of the carboxyl group to acetyl-CoA (Rendina et al, 1990;Burton et al, 1991). Multisubunit-type ACCases and cytosolic, multidomain-type ACCases are insensitive and significantly less sensitive, respectively, to CHDs and APPs than chloroplastic, multidomain-type ACCase (Egli et al, 1993;Alban et al, 1994). Thus, most plant species other than Poaceae are insensitive to these herbicides, as are most other eukaryotes and prokaryotes.…”

Wheat acetyl-coenzyme A carboxylase: cDNA and protein structure.

“…The major form was found to be located in mesophyll chloroplasts. It is also the major ACC in the endosperm and in embryos (22). Wheat ACC subunits of 220 kDa were also detected associated with leaf chloroplasts and in wheat germ (21).…”

“…The apparent lack of a transit peptide poses the question of whether and how the ACC described in this paper is transported into chloroplasts. It was shown recently that the large ACC polypeptide purifies with chloroplasts of wheat and maize (21,22). No obvious chloroplast transit peptide between the ER signal peptide and the mature protein was found in diatom ACC either (14).…”

“…Early attempts at characterization of plant ACC led to the suggestion that it consisted of low molecular weight subunits similar to those of bacteria (18). More recent efforts indicate that the plant enzyme is composed of >200-kDa subunits, similar to the enzyme from other eukaryotes (19)(20)(21)(22)(23). Plant ACC (at least one form of it) is located in plastids, the primary site of plant fatty acid synthesis, but the gene must be nuclear because no corresponding sequence has been seen in the complete chloroplast DNA sequences of tobacco, liverwort, or rice.…”