DISTRIBUTION OF THE MEVALONATE AND GLYCERALDEHYDE PHOSPHATE PYRUVATE PATHWAYS FOR ISOPRENOID BIOSYNTHESIS IN UNICELLULAR ALGAE AND THE CYANOBACTERIUM SYNECHOCYSTIS PCC-6714/
A. Disch et al., DISTRIBUTION OF THE MEVALONATE AND GLYCERALDEHYDE PHOSPHATE PYRUVATE PATHWAYS FOR ISOPRENOID BIOSYNTHESIS IN UNICELLULAR ALGAE AND THE CYANOBACTERIUM SYNECHOCYSTIS PCC-6714/, Biochemical journal, 333, 1998, pp. 381-388
Isopentenyl diphosphate, the universal isoprenoid precursor, can be pr
oduced by two different biosynthetic routes: either via the acetate/me
valonate (MVA) pathway, or via the more recently identified MVA-indepe
ndent glyceraldehyde phosphate/ pyruvate pathway. These two pathways a
re easily differentiated by incorporation of [l-C-13]glucose and analy
sis of the resulting labelling patterns found in the isoprenoids. This
method was successfully applied to several unicellular algae raised u
nder heterotrophic growth conditions and allowed for the identificatio
n of the pathways that were utilized for isoprenoid biosynthesis. All
isoprenoids examined (sterols, phytol, carotenoids) of the green algae
Chlorella fusca and Chlamydomonas reinhardtii were synthesized via th
e GAP/pyruvate pathway, as in another previously investigated green al
ga, Scenedesmus obliquus, which was also shown in this study to synthe
size ubiquinone by the same MVA-independent route. In the red alga Cya
nidium caldarium and in the Chrysophyte Ochromonas danica a clear dich
otomy was observed: as in higher plants, sterols were formed via the M
VA route, whereas chloroplast isoprenoids (phytol in Cy. caldarium and
O. danica and beta-carotene in O. danica) were synthesized via the GA
P/pyruvate route. In contrast, the Euglenophyte Euglena gracilis synth
esized ergosterol, as well as phytol, via the acetate/MVA route. Simil
ar feeding experiments were performed with the cyanobacterium Synechoc
ystis PCC 6714 using [1-C-13]- and [6-C-13]-glucose. The two isoprenoi
ds examined, phytol and beta-carotene, were shown to have the typical
labelling pattern derived from the GAP/pyruvate route.