Biochemistry Lab, Pharmacy Department, University of Genova, Genova, Italy.
Institute of Complementary and Integrative Medicine, University of Bern, Bern, Switzerland.
Adv Exp Med Biol. 2023;1438:93-99. doi: 10.1007/978-3-031-42003-0_16.
A critically important step for the uptake and transport of oxygen (O) in living organisms is the crossing of the phase boundary between gas (or water) and lipid/proteins in the cell. Classically, this transport across the phase boundary is explained as a transport by proteins or protein-based structures. In our contribution here, we want to show the significance of passive transport of O also (and in some cases probably predominantly) through lipids in many if not all aerobic organisms. In plants, the significance of lipids for gas exchange (absorption of CO and release of O) is well recognized. The leaves of plants have a cuticle layer as the last film on both sides formed by polyesters and lipids. In animals, the skin has sebum as its last layer consisting of a mixture of neutral fatty esters, cholesterol and waxes which are also at the border between the cells of the body and the air. The last cellular layers of skin are not vascularized therefore their metabolism totally depends on this extravasal O absorption, which cannot be replenished by the bloodstream. The human body absorbs about 0.5% of O through the skin. In the brain, myelin, surrounding nerve cell axons and being formed by oligodendrocytes, is most probably also responsible for enabling O transport from the extracellular space to the cells (neurons). Myelin, being not vascularized and consisting of water, lipids and proteins, seems to absorb O in order to transport it to the nerve cell axon as well as to perform extramitochondrial oxidative phosphorylation inside the myelin structure around the axons (i.e., myelin synthesizes ATP) - similarly to the metabolic process occurring in concentric multilamellar structures of cyanobacteria. Another example is the gas transport in the lung where lipids play a crucial role in the surfactant ensuring incorporation of O in the alveoli where there are lamellar body and tubular myelin which form multilayered surface films at the air-membrane border of the alveolus. According to our view, the role played by lipids in the physical absorption of gases appears to be crucial to the existence of many, if not all, of the living aerobic species.
对于生物体中氧气（O）的摄取和运输来说，至关重要的一步是跨越细胞内气体（或水）和脂质/蛋白质之间的相界。传统上，这种跨越相界的运输被解释为通过蛋白质或基于蛋白质的结构进行的运输。在我们这里的贡献中，我们希望表明，在许多（如果不是所有）需氧生物中，O 的被动运输也（并且在某些情况下可能主要是）通过脂质进行的重要性。在植物中，脂质对于气体交换（吸收 CO 和释放 O）的重要性是众所周知的。植物的叶子有一层角质层作为两侧的最后一层，由聚酯和脂质组成。在动物中，皮肤的最后一层是皮脂，由中性脂肪酯、胆固醇和蜡的混合物组成，这些物质也位于身体细胞和空气之间的边界上。皮肤的最后几个细胞层没有血管化，因此它们的新陈代谢完全依赖于这种细胞外 O 的吸收，而这种吸收不能通过血液来补充。人体通过皮肤吸收约 0.5%的 O。在大脑中，围绕神经细胞轴突形成的少突胶质细胞的髓鞘，很可能也负责使 O 从细胞外空间运输到细胞（神经元）。髓鞘没有血管化，由水、脂质和蛋白质组成，似乎吸收 O 以将其运输到神经细胞轴突，并在轴突周围的髓鞘结构内进行细胞外氧化磷酸化（即，髓鞘合成 ATP）-类似于发生在蓝细菌同心多层结构中的代谢过程。另一个例子是肺部的气体运输，其中脂质在确保 O 掺入含有板层小体和管状髓鞘的肺泡中起关键作用，这些结构形成肺泡气膜边界的多层表面膜。根据我们的观点，脂质在气体物理吸收中所起的作用对于许多（如果不是所有）需氧生物的存在似乎是至关重要的。
