The activity of acetyl-CoA carboxylase is not correlated with the rate of lipid synthesis during development of oilseed rape (Brassica napus L.) embryos
1994
Kang, F. | Ridout, C.J. | Morgan, C.L. | Rawsthorne, S.
Acetyl-CoA carboxylase (ACCase: EC 6.4.1.2) activity has been determined- in seed tissues of oilseed rape (Brassica napus L.), pea (Pisum sativum L.) and castor bean (Ricinus communis L.). A new method is described which leads to significantly higher measurable activities of the enzyme in tissue homogenates than previously reported. This method does not involve either Triton X-100 or centrifugation treatments which have been used previously in the study of the enzyme. In the case of oilseed rape the activity was also increased by removal of the testa from the seed. The activity of ACCase was determined throughout the development of oilseed rape embryos. Enzyme activity increased 3.5-fold as the embryo fresh weight increased from 0.3 to 2.0 mg and then reached a plateau at 1.1 nmol malonyl-CoA-min-1. embryo. The main period of lipid accumulation commenced at an embryo fresh weight of 2.3 mg, which was after the plateau in ACCase activity had been reached. Activity of the enzyme declined after an embryo fresh weight of 3.5 mg, which was before lipid accumulation in the embryo had been completed. Comparison of the activity of ACCase and the apparent in-vivo rate of lipid synthesis on an embryo-fresh-weight basis (i.e. nmol malonyl-CoA formed or utilized-min 1-mg fresh weight) revealed that ACCase activity declines relative to the rate of lipid synthesis throughout development. The negative correlation between these two rates is discussed in relation to the role of ACCase in the regulation of accumulation of storage lipid during embryo development.
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