Sun Z, Cunningham F X, Gantt E
Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
Proc Natl Acad Sci U S A. 1998 Sep 15;95(19):11482-8. doi: 10.1073/pnas.95.19.11482.
The enzyme isopentenyl pyrophosphate (IPP) isomerase catalyzes the reversible isomerization of IPP to produce dimethylallyl pyrophosphate, the initial substrate leading to the biosynthesis of carotenoids and many other long-chain isoprenoids. Expression of IPP isomerase, and of two enzymes specific to the carotenoid pathway (lycopene beta-cyclase and beta-carotene-C-4-oxygenase), was followed in the green unicellular alga Haematococcus pluvialis after exposure to high illumination. This alga uniquely accumulates carotenoids in the cytoplasm and in late developmental stages turns deep-red in color because of accumulation of ketocarotenoids in the cytosol. The carotenoid/chlorophyll ratio increased 3-fold in wild type and 6-fold in a precocious carotenoid-accumulating mutant (Car-3) within 24 h after increasing the illumination from 20 to 150 micromol photon m-2.s-1. Two cDNAs encoding IPP isomerase in Haematococcus, ipiHp1 and ipiHp2, were identified. Although otherwise highly similar (95% identity overall), the predicted sequence of ipiHp1 contained a 12-aa region not found in that of ipiHp2. This was reflected by a size difference between two polypeptides of 34 and 32.5 kDa, both of which reacted with an antibody to the product of ipiHp1. We suggest that the 32.5-kDa form is involved with the carotenoid accumulation in the cytoplasm, since the 32.5-kDa polypeptide was preferentially up-regulated by high light preceding the carotenoid increase and only this form was detected in red cysts.
异戊烯基焦磷酸（IPP）异构酶催化IPP的可逆异构化反应，生成二甲基烯丙基焦磷酸，这是类胡萝卜素和许多其他长链类异戊二烯生物合成的起始底物。在绿色单细胞藻类雨生红球藻暴露于高光下后，对IPP异构酶以及类胡萝卜素途径的两种特异性酶（番茄红素β-环化酶和β-胡萝卜素-C-4-加氧酶）的表达进行了跟踪研究。这种藻类独特地在细胞质中积累类胡萝卜素，在发育后期，由于细胞溶质中酮类胡萝卜素的积累而变成深红色。在光照从20微摩尔光子·平方米⁻²·秒⁻¹增加到150微摩尔光子·平方米⁻²·秒⁻¹后的24小时内，野生型中类胡萝卜素/叶绿素比值增加了3倍，早熟类胡萝卜素积累突变体（Car-3）中增加了6倍。在雨生红球藻中鉴定出了两个编码IPP异构酶的cDNA，即ipiHp1和ipiHp2。尽管它们在其他方面高度相似（总体同一性为95%），但ipiHp1的预测序列包含一个ipiHp2中未发现的12个氨基酸的区域。这反映在两种多肽大小的差异上，分别为34 kDa和32.5 kDa，两者都与ipiHp1产物的抗体发生反应。我们认为32.5 kDa的形式与细胞质中类胡萝卜素的积累有关，因为32.5 kDa的多肽在类胡萝卜素增加之前优先被高光上调，并且只有这种形式在红色囊肿中被检测到。
