Abstract
Violaxanthin de-epoxidase isolated from lettuce chloroplasts (Lactuca sativa var. Romaine) contained a single lipid component, monogalactosyldiglyceride (MG) at about 8 g per 100 g protein. The effects of MG on activation of solvent-extracted enzyme and on Km suggest that MG has two roles, namely, as a functional component of the binding site and as a substrate-solubilizing agent whose structure satisfies binding site requirements. Substrate specificity examined with various naturally occurring and semisynthetic epoxy carotenoids with known chirality showed violaxanthin de-epoxidase to be stereospecific for 3-hydroxy, 5,6-epoxy carotenoids which are in a 3S, 5R, 6S configuration. Although monoepoxides with the above configuration were active, their rates varied, apparently due to the influence of structural differences in the nonepoxide end groups. Hence while all-trans neoxanthin showed low rates, the de-epoxidation rate of antheraxanthin was 5-fold higher than violaxanthin. Neoxanthin and violeoxanthin, both naturally occurring pigments with 9-cis configurations in the acyclic polyene chain, were inactive. These effects support the view that violaxanthin de-epoxidase is a mono de-epoxidase and that the stereospecific active center is situated in a narrow well-like cavity which favors an all-trans configuration of the polyene chain. The 3-hydroxy, 5,6-epoxy group of the naturally occurring pigments, diadinoxanthin, antheraxanthin, and β-cryptoxanthin epoxide are assumed to be the 3S, 5R, 6S configuration based on their reactivity with violaxanthin de-epoxidase.
Original language | English |
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Pages (from-to) | 514-522 |
Number of pages | 9 |
Journal | Archives of Biochemistry and Biophysics |
Volume | 190 |
Issue number | 2 |
DOIs | |
State | Published - Oct 1978 |
Bibliographical note
Funding Information:‘This work was supported in part by National Science Foundation Grant PCM 7513126 AOl. Journal Series No. 1972 of the Hawaii Agricultural Experiment Station. ’ To whom correspondence should be addressed.
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Molecular Biology