The murburn precepts for photoreception

K. Manoj, Vivian David Jacob
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引用次数: 16

Abstract

Murburn concept is a redox mechanistic scheme involving interactive equilibriums of discretized or organized proteins/substrates molecules, unbound ions and radicals (or reactive species); which may afford selective/specific electron transfers, particularly at phospholipid interfaces. Earlier, we have applied murburn concept to provide parsimonious explanations (grounded in thermodynamics and kinetics) for various physiological/bioenergetic routines like xenobiotic metabolism, unusual dose responses, aerobic respiration, thermogenesis, homeostasis, trans-membrane potential, oxygenic photosynthesis, etc. While proposing the murburn model for photophosphorylation, we had projected that the murburn mechanism could also be relevant for photoreception physiology. Herein, we expand on this aspect and present the basic scheme and evidence in support for the murburn model of photoreception, with retinal/opsin as the salient photon-impingement response-transducing element. In alignment with our earlier murburn schemes, we propose that diffusible reactive oxygen species (DROS, as exemplified by superoxide, which is currently deemed a toxic product of all-trans retinal and NADPH oxidase interactions) is produced in rod/cone cells upon photoactivation and it plays a crucial role in the visual cycle. This is supported by the fact that layers of photoreceptive neural cells precede the rod/cone cells (with respect to the presentation to oncoming light ray/photon), there exists high oxygen demand in retina, copious ROS are detected in functional retina, NAD(P)H/reductase is involved in the cycle, events occur at sub-micrometer dimensioned phospholipid disks stacked to stabilize DROS and minimize free protons (quite like the thylakoids that harbor carotenoids in chloroplasts and cyanobacteria), etc. In the new scheme, photo-electric activation leads to charge separation and hyperpolarization. This electro-chemical signaling serves is the front-runner to a trigger for action potential relay along a neuron and the superoxide mediated phosphorylation of GDP bound to transducin serves as the initiator of signal transduction cascade. The newly proposed scheme allows a facile electrical connectivity of the retina-photoreceptors with the brain via the optic nerve, and is anatomically correlated with the structure and resolution or retina, and is kinetically viable.
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默伯恩的感光戒律
Murburn概念是一种氧化还原机制方案,涉及离散或有组织的蛋白质/底物分子、未结合的离子和自由基(或活性物质)的相互作用平衡;它可以提供选择性/特异性电子转移,特别是在磷脂界面上。在此之前,我们已经应用murburn概念(基于热力学和动力学)为各种生理/生物能量过程(如异种代谢、异常剂量反应、有氧呼吸、产热、体内平衡、跨膜电位、含氧光合作用等)提供了简明的解释。在提出光磷酸化的murburn模型时,我们预测murburn机制也可能与光接受生理学有关。在此,我们对这方面进行了扩展,并提出了支持murburn光接受模型的基本方案和证据,其中视网膜/视蛋白是显著的光子撞击反应传导元件。与我们早期的murburn方案一致,我们提出,在光激活后,视杆/视锥细胞会产生扩散活性氧(DROS,如超氧化物,目前被认为是全反式视网膜和NADPH氧化酶相互作用的有毒产物),它在视觉循环中起着至关重要的作用。这是由以下事实支持的:感光神经细胞层在杆状/锥状细胞之前(关于对入射光线/光子的呈现),视网膜中存在高氧需求,在功能视网膜中检测到丰富的活性氧,NAD(P)H/还原酶参与循环,事件发生在亚微米尺寸的磷脂盘堆积以稳定活性氧并减少自由质子(很像叶绿体和蓝藻中含有类胡萝卜素的类囊体)。等。在新方案中,光电活化导致电荷分离和超极化。这种电化学信号是沿神经元的动作电位接力的触发者,而与转导蛋白结合的超氧化物介导的GDP磷酸化是信号转导级联的启动者。新提出的方案允许视网膜光感受器通过视神经与大脑进行简单的电连接,并且在解剖学上与视网膜的结构和分辨率相关,并且在动力学上可行。
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