Ketocarotenoid biosynthesis outside of plastids in the unicellular green alga Haematococcus pluvialis

Citation
K. Grunewald et al., Ketocarotenoid biosynthesis outside of plastids in the unicellular green alga Haematococcus pluvialis, J BIOL CHEM, 276(8), 2001, pp. 6023-6029
Citations number
38
Categorie Soggetti
Biochemistry & Biophysics
Journal title
JOURNAL OF BIOLOGICAL CHEMISTRY
ISSN journal
00219258 → ACNP
Volume
276
Issue
8
Year of publication
2001
Pages
6023 - 6029
Database
ISI
SICI code
0021-9258(20010223)276:8<6023:KBOOPI>2.0.ZU;2-5
Abstract
The carotenoid biosynthetic pathway in algae and plants takes place within plastids. In these organelles, carotenoids occur either in a free form or b ound to proteins. Under stress, the unicellular green alga Haematococcus pl uvialis accumulates secondary carotenoids, mainly astaxanthin esters, in cy toplasmic lipid vesicles up to 4% of its dry mass. It is therefore one of t he favored organisms for the biotechnological production of these antioxida tive compounds. We have studied the cellular localization and regulation of the enzyme beta -carotene oxygenase in H. pluvialis that catalyzes the int roduction of keto functions at position C-4 of the beta -ionone ring of bet a -carotene and zeaxanthin, Using immunogold labeling of ultrathin sections and Western blot analysis of cell fractions, we discovered that under indu ctive conditions, beta -carotene oxygenase was localized both in the chloro plast and in the cytoplasmic lipid vesicles, which are (according to their lipid composition) derived from cytoplasmic membranes. However, p-carotene oxygenase activity was confined to the lipid vesicle compartment, Because a n early carotenogenic enzyme in the pathway, phytoene desaturase, was found only in the chloroplast (Grunewald, K,, Eckert, M., Hirschberg, J,, and Ha gen, C, (2000) Plant Physiol. 122, 1261-1268), a transport of intermediates from the site of early biosynthetic steps in the chloroplast to the site o f oxygenation and accumulation in cytoplasmic lipid vesicles is proposed.