Beale S I, Cornejo J
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912.
J Biol Chem. 1991 Nov 25;266(33):22328-32.
Cell-free extract of the unicellular rhodophyte, Cyanidium caldarium catalyzes enzymatic reduction of biliverdin IX alpha to phycocyanobilin, the chromophore of the light-harvesting phycobiliprotein, phycocyanin. The enzyme activity is soluble, and the required reductant is NADPH. The extract has been separated into three protein fractions, all of which are required to reconstitute biliverdin reduction. One fraction contains ferredoxin, which was identified by its absorption spectrum. This fraction could be replaced with commercial ferredoxin derived from spinach or the red alga, Porphyra umbilicalis. The second protein fraction contains ferredoxin-NADP+ reductase, which was identified by the ability to catalyze ferredoxin-dependent reduction of cytochrome c in the presence of NADPH. This fraction could be replaced with commercial spinach ferredoxin-NADP+ reductase. These two components appear to be identical to previously described components of the algal heme oxygenase system that catalyzes biliverdin IX alpha formation from protoheme in C. caldarium extracts. The third protein fraction, in the presence of the first two (or their commercial counterparts) plus NADPH, catalyzes the reduction of biliverdin IX alpha to phycocyanobilin. The results indicate that the transformation of biliverdin to phycocyanobilin catalyzed by C. caldarium extracts is a ferredoxin-linked reduction process. The results also suggest the possibility that heme oxygenation and biliverdin reduction may occur in C. caldarium on associated enzyme systems.
单细胞红藻嗜热蓝藻的无细胞提取物催化胆绿素IXα酶促还原为藻蓝胆素，藻蓝胆素是捕光藻胆蛋白藻蓝蛋白的发色团。该酶活性是可溶的，所需的还原剂是NADPH。提取物已被分离成三个蛋白质组分，所有这些组分都是重建胆绿素还原所必需的。一个组分含有铁氧还蛋白，通过其吸收光谱鉴定。该组分可用源自菠菜或红藻紫菜的商业铁氧还蛋白替代。第二个蛋白质组分含有铁氧还蛋白-NADP +还原酶，通过在NADPH存在下催化铁氧还蛋白依赖性细胞色素c还原的能力来鉴定。该组分可用商业菠菜铁氧还蛋白-NADP +还原酶替代。这两种成分似乎与先前描述的藻类血红素加氧酶系统的成分相同，该系统催化嗜热蓝藻提取物中原血红素形成胆绿素IXα。第三个蛋白质组分在前两个（或其商业对应物）加NADPH存在下，催化胆绿素IXα还原为藻蓝胆素。结果表明，嗜热蓝藻提取物催化的胆绿素向藻蓝胆素的转化是一个铁氧还蛋白连接的还原过程。结果还表明，嗜热蓝藻中血红素氧化和胆绿素还原可能发生在相关酶系统上。
