|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥1,600,000 (Direct Cost : ¥1,600,000)
A ketocarotenoid called astaxanthin synthesized by a unicellular green alga Haematococcus pluvialis was shown to possess antioxidant activity higher than beta-carotene and vitamin E.When active oxygen speices such as H_2O_2 and superoxide was added to the algal resting stage cell, a cyst, we have found that high amount of astaxanthin was synthesized without de nova protein synthesis. In this study, we aimed to characterize this control system of the activation mechanism of the carotenoid biosynthesis.
Firstly, 3-hydroxymethylglutaryl coenzyme A reductase (HMGR) involved in the early isoprenoid biosynthetic stage was focused, and when algal cyst was treated with HMGR-specific inhibitor, compactin, it was found that carotenoid formation was completely blocked, whereas uninhibited at all with the simultaneous presence of active oxygen species. The result suggested that HMGR would be a target entry point of oxidative stress response. In addition, with extensive screening of compactive-resistant strains of the alga far the enhanced astaxanthin production, the mutants was found to exhibit similar specific, activities with a slightly higher Ki value.
Secondly, as the final astaxanthin biosynthesis, hydroxylation and oxygenation at beta-carotene molecule was investigated in uitro. Although at least seven intermediate carotenoid species would be involved, little was known at the enzymatic levels, it was firstly shown that beta-carotene was converted to zeaxanthin only in the presence of NADPH and atomospheric oxygen with cell-free membrane bound fraction of the alga by a HPLC with a highly sensitive photodiode-array detector.