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Acetyl-coenzyme A carboxylase from avocado (Persea americana) plastids and spinach (Spinacia oleracea) chloroplasts.

ABSTRACT: Preparations of acetyl-CoA carboxylase [acetyl-CoA-carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] have been obtained from the plastids of avocado (Persea americana) fruit mesocarp and from spinach (Spinacia oleracea) chloroplasts. Both preparations required bovine serum albumin, HCO3-, citrate and glycerol for stabilization. The molecular weight of the avocado enzyme was about 6.5 X 10(5) on the basis of 1 mol of biotin/mol of enzyme, the behaviour of both enzymes on gel filtration being in accord with such a value. Removal of the stabilizing bovine serum albumin resulted in the loss of a biotin-containing fragment from the avocado enzyme. Citrate stabilized the enzyme at 10 mM and activated it optimally at 3.0 mM, effecting an approx. 2-fold increase in Vmax. It is suggested that in vivo the enzyme may be located within the chloroplast lamellae.

SUBMITTER: Mohan SB

PROVIDER: S-EPMC1162450 | biostudies-other | 1980 Jun

REPOSITORIES: biostudies-other

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Project description:1. Chloroplasts isolated from spinach leaves by using the low-ionic-strength buffers of Nakatani & Barber [(1977) Biochim. Biophys. Acta.461, 510-512] had higher rates of HCO(3) (-)-dependent oxygen evolution (up to 369mumol/h per mg of chlorophyll) and higher rates of [1-(14)C]acetate incorporation into long-chain fatty acids (up to 1500nmol/h per mg of chlorophyll) than chloroplasts isolated by using alternative procedures. 2. Acetate appeared to be the preferred substrate for fatty acid synthesis by isolated chloroplasts, although high rates of synthesis were also measured from H(14)CO(3) (-) in assays permitting high rats of photosynthesis. Incorporation of H(14)CO(3) (-) into fatty acids was decreased by relatively low concentrations of unlabelled acetate. Acetyl-CoA synthetase activity was present 3-4 times in excess of that required to account for rates of [1-(14)C]acetate incorporation into fatty acids, but pyruvate dehydrogenase was either absent or present in very low activity in spinach chloroplasts. 3. Rates of long-chain-fatty acid synthesis from [1-(14)C]acetate in the highly active chloroplast preparations, compared with those used previously, were less dependent on added cofactors, but showed a greater response to light. The effects of added CoA plus ATP, Triton X-100 and sn-glycerol 3-phosphate on the products of [1-(14)C]acetate incorporation were similar to those reported for less active chloroplast preparations. 4. Endogenous [(14)C]acetyl-CoA plus [(14)C]malonyl-CoA was maintained at a constant low level even when fatty acid synthesis was limited by low HCO(3) (-) concentrations. Endogenous [(14)C]acyl-(acyl-carrier protein) concentrations increased with increasing HCO(3) (-) concentration and higher rates of fatty acid synthesis, but were slightly lower in the presence of Triton X-100. It is proposed that rates of long-chain-fatty acid synthesis in isolated chloroplasts at saturating [1-(14)C]acetate concentrations and optimal HCO(3) (-) concentrations may be primarily controlled by rates of removal of the products of the fatty acid synthetase.

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Acetyl-coenzyme A carboxylase from avocado (Persea americana) plastids and spinach (Spinacia oleracea) chloroplasts.

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