Biliverdin Amides Reveal Roles for Propionate Side Chains in Bilin Reductase Recognition and in Holophytochrome Assembly and Photoconversion
摘要:
Linear tetrapyrroles (bilins) perform important antioxidant and light-harvesting functions in cells from bacteria to humans. To explore the role of the propionate moieties in bilin metabolism, we report the semisynthesis of mono- and diamides of biliverdin IX alpha and those of its non-natural XIII alpha isomer. Initially, these were examined as substrates of two types of NADPH-dependent biliverdin reductase, BVR and BvdR, and of the representative ferredoxin-dependent bilin reductase, phycocyanobilin:ferredoxin oxidoreductase (PcyA). Our studies indicate that the NADPH-dependent biliverdin reductases are less accommodating to amidation of the propionic acid side chains of biliverdin IX alpha than PcyA, which does not require free carboxylic acid side chains to yield its phytobilin product, phycocyanobilin. Bilin amides were also assembled with BV-type and phytobilin-type apophytochromes, demonstrating a role for the 8-propionate in the formation of the spectroscopically native P-r dark states of these biliprotein photosensors. Neither ionizable propionate side chain proved to be essential to primary photoisomerization for both classes of phytochromes, but an unsubstituted 12-propionate was required for full photointerconversion of phytobilin-type phytochrome Cph1. Taken together, these studies provide insight into the roles of the ionizable propionate side chains in substrate discrimination by two bilin reductase families while further underscoring the mechanistic differences between the photoconversions of BV-type and phytobilin-type phytochromes.
(Chloro)platinum(III)protoporphyrin and its closest noncyclic analogue, platinum(III)biliverdin, are synthesized; the forms and stability of the complexes in proton-donating solutions as dependent on temperature and solvent composition are studied. The macrocyclic effect (the effect of coordinated macrocyclic ligand opening) is directly estimated quantitatively; a correlation between its contribution to the rate of dissociation (or stability) of the complexes and their structures is found.
Pyrolyzed photoresist carbon electrodes (PPCEs) are fabricated by the photopatterning of a negative tone epoxy-based photoresist, SU-8, through optimized standard UV photolithography. The electrochemical characteristics of PPCEs are investigated in dimethyl sulfoxide (DMSO), observing a wider accessible potential window and a smaller capacitance with respect to glassy carbon electrodes. PPCEs are used to study
borylation and cross-coupling chemistries, translated into the concise assembly of the structurally diverse bilirubin oxidationproducts (BOXes, propentdyopents, and biopyrrins). The discovery of a new photoisomer of biopyrrin A named lumipyrrin is reported. Synthetic bilirubin oxidationproducts made available in sufficient purity and quantity will support future in vitro and in vivo investigations.
胆红素是血红素分解代谢的主要产物。高浓度的色素具有神经毒性,但稍微升高浓度则有益。作为一种有效的抗氧化剂,胆红素在体内发生氧化转化并产生各种氧化片段。它们的形成机制、内在的生物活性以及在人类病理生理学中的潜在作用尚不清楚。降解方法已用于获取胆红素氧化产物的样品以供研究。在这里,我们报告了一种补充的、全合成的制备方法。我们的策略利用母体四环颜料中的重复取代模式。设计并有效合成了功能化的可偶联γ-内酯、γ-内酰胺和吡咯单环结构单元。随后的模块化组合,在金属催化的硼化和交叉偶联化学的支持下,转化为结构多样的胆红素氧化产物(BOX、propentdyopents和biopyrrins)的简洁组装。据报道,发现了一种新的生物比林 A 光异构体,名为 lumipyrrin。足够纯度和数量的合成胆红素氧化产物将支持未来的体外和体内研究。