Violaxanthin de-epoxidase. Lipid composition and substrate specificity

H. Y. Yamamoto, R. M. Higashi

Research output: Contribution to journalArticlepeer-review

154 Scopus citations

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 languageEnglish
Pages (from-to)514-522
Number of pages9
JournalArchives of Biochemistry and Biophysics
Volume190
Issue number2
DOIs
StatePublished - 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

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