Properties and morphology of barley embryo acetyl CoA carboxylase

Brock, Kaye E.; Kannangara, C. Gamini

doi:10.1007/bf02906537

Cited by 24 publications

(12 citation statements)

References 18 publications

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“…The enzyme activities of the whole tissue homogenate ofembryo isolates from 1-day seedlings (Table I) are comparable to those reported for wheat germ (13) and barley embryo extracts (6). The increased activity during development (Table I) (31) on studies with developing leaves of Chl-deficient barley mutants were in agreement with this in that the enzyme activities of the mutants they studied remained below those of the wild type.…”

Section: Discussionsupporting

confidence: 80%

“…Biotin estimations as performed were presumed adequate for the ted 3 mi with localization of the acetyl-CoA carboxylase because it is the only C03 then was biotin enzyme described for plants. The biotin levels of 1.0 to 3.1 pg/mg protein (Table IX) exceed those reported for purified barley-embryo acetyl-CoA carboxylase (6); however, they are somewhat less than the biotin content of purified BCCP (6,10). The high readings obtained probably reflect a high free-biotin content in the chloroplast stromal preparations.…”

Section: 495mentioning

confidence: 53%

“…For analysis of seeds germinated for I and 2 days, the embryos were excised from the endosperms, whereas whole shoots from 3-and 4-day-old seedlings were excised at the point of seed attachment. To facilitate the isolation of embryos, the seeds were dehusked essentially as described by Brock and Kannangara (6) used for the analysis of 4'-, 5'-, and 6'-day-old seedlings (Table I) and for plastid isolation of 4-, 6-, and 8-day-old seedlings (Table V) The specific radioactivity, in dpm/,umol, of the NaH"4CO3 solution was determined as outlined by Miller and Levy (26). Protein estimations were determined by the method of Bradford (5) with BSA fraction V as the standard, and Chl was determined according to Arnon (2).…”

mentioning

confidence: 99%

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Acetyl Coenzyme A Carboxylase Activity in Developing Seedlings and Chloroplasts of Barley and Its Virescens Mutant

Thomson¹,

Zalik²

1981

Plant Physiol.

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Acetyl coenzyme A (CoA) carboxylase activity of whole tissue homogenates and chloroplast preparations was analyzed as the acetyl-CoA-dependent incorporation of I'4Cibicarbonate into an acid-stable product. The absolute requirement for ATP and MgCl2, the complete inhibition with avidin, and end-product analysis were consistent with the presence of acetyl-CoA carboxylase activity. Little difference was found between the mutant and normal tissue homogenates from the 1-to 3-day growth stages, during which period both showed a 3-fold increase. However, by 4 days, the activity of the mutant exceeded that of the normal. Fractionation studies showed that the enzyme was a soluble protein present in the stromal fraction of chloroplasts. The biotin content was also highest in the stroma, although it was found in the lamellar fraction as well. For both the mutant and the normal, the highest acetyl-CoA carboxylase activities were obtained in the stromal preparations from 4-day seedlings (54 and 31 nmoles per milligram protein per minute for the mutant and the normal, respectively) with a progressive decline by 6 and 8 days. The difference between the mutant and the normal was not due to the accumulation of an inhibitor in the normal.Acetyl-CoA carboxylase catalyzes the formation of malonylCoA which, in turn, is utilized by the fatty-acid synthetase complex for the de novo synthesis of fatty acids (23,33). The enzyme has been purified from wheat germ (13), barley embryos (6), a variety of animal tissues, yeast, and microorganisms (23). All the carboxylases studied were shown to contain definable subunits, and the animal and yeast complexes required SDS and urea treatment for dissociation, which resulted in inactivation; however, the Escherichia coli enzyme complex was readily dissociable into active subunits and the partial reactions have been primarly defined by the study of the E. coli system (35 Even though chloroplasts are the major or sole site of cellular fatty acid synthesis in green tissue (29), the presence of acetylCoA carboxylase in the chloroplast fraction has only been ascribed through indirect methods. Reports describing acetyl-CoA carboxylase activity in green tissue and in isolated chloroplasts are limited, but intact chloroplasts readily incorporate acetate into palmitic and oleic acid by de novo synthesis (12,33), suggesting that the enzyme is functioning effectively. Acetate and acetyl-CoA served as poor substrates for broken chloroplasts, whereas malonyl-CoA was readily incorporated into fatty acids (33). This dicrepancy was partially explained by the occurrence of an unidentified inhibitor in disrupted lettuce and spinach chloroplast fractions (33). The buildup of an inhibitor was also suggested from studies of plastids isolated from greening barley seedlings (18). Good acetyl-CoA carboxylase activity was detected if the disrupted spinach chloroplast system was supplemented with E. coli carboxyltransferase, suggesting the inhibitor was specific for the CT reaction (21). The procaryotic nature of t...

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Section: Discussionsupporting

confidence: 80%

Section: 495mentioning

confidence: 53%

mentioning

confidence: 99%

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Acetyl Coenzyme A Carboxylase Activity in Developing Seedlings and Chloroplasts of Barley and Its Virescens Mutant

Thomson¹,

Zalik²

1981

Plant Physiol.

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“…Although the subunit size in animals, yeast and plants is > 200 kDa there have been reports of much smaller (50,60 or 75 kDa) subunits being present in certain plant tissues [6,20,[32][33][34][35][36][37]46]. In animals the enzyme exists in the cytoplasm and is subject to complex regulatory mechanisms including multi-site phosphorylation [12].…”

Section: Introductionmentioning

confidence: 99%

Molecular cloning of two different cDNAs for maize acetyl CoA carboxylase

1994

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Acetyl CoA carboxylase (EC 6.4.1.2) in plants is a chloroplast-localized, biotin-containing enzyme that catalyses the carboxylation of acetyl CoA to malonyl CoA, the first committed step of the fatty acid biosynthesis pathway. Acetyl CoA carboxylase is the target site for the monocotyledon-specific aryloxyphenoxypropionate and cyclohexanedione groups of herbicides. We have purified a herbicide-sensitive acetyl CoA carboxylase from maize leaves to homogeneity (specific activity 7 mumol min-1 mg-1), separating it during the purification from a minor herbicide-resistant acetyl CoA carboxylase. The purified enzyme is a dimer of 230 kDa subunits. Antibodies raised to the purified acetyl CoA carboxylase detected three cross-reacting clones in a maize leaf cDNA expression library, each having an insert of 4-4.5 kb. Restriction analysis and sequencing showed that the cDNAs were derived from two different transcripts. Comparison of the deduced amino acid sequences with those of chicken and yeast acetyl CoA carboxylases confirmed that both types encoded acetyl CoA carboxylase, corresponding to the C-terminal half of the enzyme. The overall identity of the maize and chicken sequences was 37% (58% similarity) but for some shorter regions was much higher. Analysis of six other acetyl CoA carboxylase clones recovered from the maize cDNA library showed four belonged to one type and two to the other. The nucleotide sequence similarity between the two types of cDNA was approximately 95% in the coding region but considerably less in the 3'-untranslated region. Northern blot analysis of maize RNA showed a single band of 8.2-8.5 kb for acetyl CoA carboxylase mRNA. Southern blot hybridisations indicated that there are probably no more than two genes in maize for acetyl CoA carboxylase. The possible significance of two different cDNAs for acetyl CoA carboxylase is discussed.

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“…The structure of plant acetyl-CoA carboxylases is unclear since acetyl-CoA carboxylases with biotin-containing subunits, ranging from 21 to 240 kDa, have been reported (67)(68)(69)(70)(71)(72)(73)(74)(75)(76). A number of studies have reported the purification of acetyl-CoA carboxylases containing a large, 220 kDa, biotin-containing subunit (74)(75)(76).…”

Section: Properties Of Plant Biotin-containing Enzymesmentioning

confidence: 99%

Biochemical characterization of plant biotin-containing enzymes

Diez

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Properties and morphology of barley embryo acetyl CoA carboxylase

Cited by 24 publications

References 18 publications

Acetyl Coenzyme A Carboxylase Activity in Developing Seedlings and Chloroplasts of Barley and Its Virescens Mutant

Acetyl Coenzyme A Carboxylase Activity in Developing Seedlings and Chloroplasts of Barley and Its Virescens Mutant

Molecular cloning of two different cDNAs for maize acetyl CoA carboxylase

Biochemical characterization of plant biotin-containing enzymes

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