Fairchild C D, Glazer A N
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
J Biol Chem. 1994 Nov 18;269(46):28988-96.
C-Phycoerythrin is a light-harvesting protein whose alpha and beta subunits carry thioether-linked phycoerythrobilin (PEB) at cysteine residues alpha-82, alpha-139, beta-48,59 (doubly-linked), beta-80, and beta-165. The two subunits of Calothrix sp. PCC 7601 C-phycoerythrin, overexpressed together as apopolypeptides in Escherichia coli, formed inclusion bodies. Purified apo-alpha was soluble in the absence of urea, whereas the apo-beta subunit was only soluble at high urea concentrations. Products of nonenzymatic addition of PEB and phycocyanobilin (PCB) to apo-alpha were characterized by isolation of bilin peptides and spectroscopy. Reaction of PEB with the apo-alpha subunit led primarily to 15,16-dihydrobiliverdin (Cys-82) or urobilin (Cys-139) adducts, and small amounts of the natural PEB adducts at both Cys-82 and Cys-139. PCB reacted primarily with Cys-82 to form phycocyanobilin and mesobiliverdin adducts. Both PEB and PCB also formed relatively small amounts of adducts with Cys-59, which is not a bilin attachment residue in natural phycoerythrin. Sodium azide was found to promote the addition of PEB to simple thiols but not to apo-alpha phycoerythrin.
藻红蛋白是一种捕光蛋白，其α和β亚基在半胱氨酸残基α-82、α-139、β-48、59（双连接）、β-80和β-165处携带硫醚连接的藻红素（PEB）。集胞藻属PCC 7601藻红蛋白的两个亚基作为脱辅基多肽在大肠杆菌中共同过量表达，形成了包涵体。纯化的脱辅基α亚基在没有尿素的情况下可溶，而脱辅基β亚基仅在高尿素浓度下可溶。通过分离胆素肽和光谱对PEB和藻蓝胆素（PCB）非酶促添加到脱辅基α亚基的产物进行了表征。PEB与脱辅基α亚基的反应主要产生15,16-二氢胆绿素（Cys-82）或尿胆素（Cys-139）加合物，以及少量在Cys-82和Cys-139处的天然PEB加合物。PCB主要与Cys-82反应形成藻蓝胆素和中胆绿素加合物。PEB和PCB也与Cys-59形成相对少量的加合物，Cys-59在天然藻红蛋白中不是胆素连接残基。发现叠氮化钠可促进PEB添加到简单硫醇中，但不能促进其添加到脱辅基α藻红蛋白中。
