Carotenoid Cyclase Enzymes from Arabidopsis thaliana: Structure, Function, and Interactions

点击翻译按钮获取中文摘要

9631257 Cunningham The cyclization of lycopene is a key branch point in the pathway carotenoid biosynthesis. Two types of cyclic end groups are commonly found in higher plant carotenoids: the ( and ( cyclase enzymes are encoded by homologous genes in Arabidopsis thaliana, and both enzymes us the linear, symmetrical lycopene as a substrate. However, the ( cyclase adds only one ring while the ( cyclase introduces a ring at both ends of the molecule. The objectives of this research are to examine and compare substrate utilization and product formation by the ( and ( cyclases of A. thaliana, to identify functional regions and amino acid residues within these two enzymes, and to ascertain whether cyclase-cyclase interactions play a role in enzyme function. Carotenoids with cyclic end groups are essential components of the photosynthetic membranes in all plants, algae and cyanobacteria. These lipid-soluble compounds protect against photooxidation, harvest light for photosynthesis, and dissipate excess light energy absorbed by the antenna pigments. The accumulation of carotenoid pigments in the photosynthetic membranes is closely coordinated with the biosynthesis and assembly of the photosynthetic apparatus. The regulatory mechanisms that serve to coordinated these processes are obscure. The classical biochemical approaches have been of limited value in the study of the membrane-associated enzymes of the carotenoid pathway, therefore the approach to be taken is largely a genetic one. The results of this research will provide valuable information on the operation and control of the essential plant pathway of carotenoid biosynthesis, and can provide insights on the functioning and regulation of other metabolic pathways that involve membrane-associated multienzyme complexes.