BIOSYNTHESIS OF UNUSUAL ACYCLIC ISOPRENOIDS IN THE ALGA BOTRYOCOCCUS BRAUNII

Article abstract of DOI:10.1016/S0031-9422(00)84886-4

A 'resting state' isolate of the hydrocarbon-producing alga Botryococcus braunii photoassimilated sodium <¹⁴C>bicarbonate at rates comparable to fast growing algae, such as Chlorella ( > 150 μg atoms ¹⁴C/mg chlorophyll hr).Early in the reaction (up to several min), most of the radioactivity was associated with water-soluble metabolites.However, labeling of hexane-soluble compounds steadily increased from ca 3 percent at 15 sec to over 50 percent of the total incorporated ¹⁴C at 60 min.The purified hexane fraction, which consisted of a series of botryococcenes and squalene, constituted a relatively constant proportion (40-45percent) of the total hexane-soluble radioactivity at all bur the earliest time points ( < 60 sec).This fraction initially consisted almost exclusively of a C₃₀ botryococcene (ca 91 percent) and squalene (ca 8 percent); however, small amounts of radioactivity sequentially appeared in the C₃₁, C₃₂ and C₃₄ botryococcenes.The results of pulse-chase experiments implicated the C₃₀ botryococcene as the precursor of the higher homologues; during the chase, loss of radioactivity from the C₃₀ compound was accompanied by a concomitant increase in the labelling of the C₃₁ and C₃₂ compounds.This study provides further evidence that the relatively slow growth of Botryococcus in culture may result, in part, from the diversion of a large proportion of reduced carbon into energetically expensive compounds and that the slower growth rate in the 'resting state' cannot be totally attributed to an impaired or intrinsically slow metabolism. - Key Wor Index - Botryococcus braunii; Chlorophyceae; alga; biosynthesis acyclic isoprenoids; botryococcenes.