Cornejo J, Willows R D, Beale S I
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
Plant J. 1998 Jul;15(1):99-107. doi: 10.1046/j.1365-313x.1998.00186.x.
The phytobilin chromophores of phycobiliproteins and phytochromes are biosynthesized from heme in a pathway that begins with the opening of the tetrapyrrole macrocycle of protoheme to form biliverdin IX alpha, in a reaction catalyzed by heme oxygenase. A gene containing an open reading frame with a predicted polypeptide that has a sequence similar to that of a conserved region of animal microsomal heme oxygenases was identified in the published genomic sequence of Synechocystis sp. PCC 6803. This gene, named ho1, was cloned and expressed in Escherichia coli under the control of the lacZ promoter. Cells expressing the gene became green colored due to the accumulation of biliverdin IX alpha. The size of the expressed protein was equal to the predicted size of the Synechocystis gene product, named HO1. Heme oxygenase activity was assayed in incubations containing extract of transformed E. coli cells. Incubations containing extract of induced cells, but not those containing extract of uninduced cells, had ferredoxin-dependent heme oxygenase activity. With mesoheme as the substrate, the reaction product was identified as mesobiliverdin IX alpha by spectrophotometry and reverse-phase HPLC. Heme oxygenase activity was not sedimented by centrifugation at 100, 000 g. Expression of HO1 increased several-fold during incubation of the cells for 72 h in iron-deficient medium.
藻胆蛋白和光敏色素的藻胆素发色团是由血红素通过一条生物合成途径生成的，该途径始于原血红素的四吡咯大环在血红素加氧酶催化的反应中打开，形成胆绿素IXα。在集胞藻属PCC 6803已发表的基因组序列中，鉴定出一个基因，其开放阅读框预测的多肽序列与动物微粒体血红素加氧酶保守区域的序列相似。这个名为ho1的基因被克隆，并在lacZ启动子的控制下在大肠杆菌中表达。由于胆绿素IXα的积累，表达该基因的细胞变成了绿色。表达蛋白的大小与集胞藻基因产物HO1的预测大小相等。在含有转化大肠杆菌细胞提取物的孵育体系中测定血红素加氧酶活性。含有诱导细胞提取物的孵育体系具有铁氧还蛋白依赖性血红素加氧酶活性，而含有未诱导细胞提取物的孵育体系则没有。以中血红素为底物，通过分光光度法和反相高效液相色谱法将反应产物鉴定为中胆绿素IXα。血红素加氧酶活性不会在十万倍重力下离心沉淀。在缺铁培养基中培养细胞72小时期间，HO1的表达增加了几倍。
