As the main bioenergetically active organelles of nonphotosynthetic eukaryotes, mitochondria convert part of the free energy released by the oxidation of nutrient molecules into ATP and other useful forms of energy needed by cells. However, this energy conversion process is far from being 100% efficient, and a significant fraction of the released energy is dissipated as heat. This raises the hitherto unexplored question of the effect of this heat production on the temperature of mitochondria and other cellular components.
Molecular machines: What about turbulent motion in the vicinity of proteins? Respiratory proteins are extraordinary nanoscale molecular machines that can change their conformational state hundreds of times per second; the ATP synthase rotates at up to 400 times per second.
Endothermy is generated by the simple expedient of having about five times as many mitochondria in the visceral organs as equivalent poikilotherms, which, in evolutionary terms, may have originally been associated with greater stamina and a higher field metabolic rate.
“Although thermogenesis defines the warm-blooded lifestyle and is the reason that many birds and mammals remain active in winter, there is only one known example of poikilotherms that keep themselves warm in the winter by producing metabolic heat and that is honeybees (Southwick, 1991). Honeybee colonies can maintain core temperatures of 34-35°C over the brood area despite air temperatures outside the hive that may be far below 0°C. Their success is due to their social behavior including clustering, thermoregulation and food hoarding. The greater the ratio of body surface area to mass (SA/M), the higher the rate of heat loss. Clustering greatly reduces the SA/M so that the SA/M of a clustered colony can be <5% of that of an individual bee. With the improved heat retention that this allows, it is then feasible to heat the colony. This is done via shivering, a form of muscle contraction that does no mechanical work but releases large amounts of heat from the hydrolysis of adenosine triphosphate (ATP). By modulating the number of bees shivering and the packing of the cluster, colony temperature is very precisely regulated. High rates of sugar oxidation by thoracic flight muscles are required to support shivering and this is also only possible because of another social behaviour of the colony, the huge stores of honey that are accumulated over the summer months.”
Caffeine — the most often consumed stimulant in the world—blocks adenosine receptors and normally attenuates the consequences of sleep deprivation on arousal, vigilance, and attention. Caffeine acts as a non-selective, competitive antagonist at A1 and A2A receptors.
Endothelial hemoglobin a is enriched at the myoendothelial junction, the point where endothelial cells and smooth muscle cells make contact in resistance arteries and arterioles, where it regulates the effect of NO signaling on vascular reactivity. Mechanistically, hemoglobin a heme iron in the Fe3+ state permits active NO signaling, and this signaling is shut off when hemoglobin a is reduced to the Fe2+ state by endothelial cytochrome B5 reductase 3. - Straub lab
Hemoglobin (Hb) is a major protein involved in transport of oxygen (O2). Red blood cells (RBCs) contain maximum amount of Hb and because of their unique structure and plasticity they transport O2 to various tissues of the body at an optimal concentration. Recently, it has been reported that, apart from RBCs, Hb is also expressed by nonerythroid cells such as epithelial cells of different origin. The cells expressing Hb are from the tissues where maintenance of O2 homeostasis is of paramount importance. Hb expression has been observed in the epithelial cells from human tissues including lungs, neurons, retina, and endometrium.
Hemoglobin was accidentally discovered by Hünefeld in 1840 in samples of earthworm blood held under two glass slides. He occasionally found small plate-like crystals in desiccated swine or human blood samples. These crystals were later named as “Haemoglobin” by Hoppe-Seyler in 1864. Around 1870, Claude Bernard discovered its role as oxygen carrier. However the discovery of the detailed three-dimensional structure of Hb by X-ray crystallography is credited to Perutz et al. for which he was awarded the Nobel Prize (1962) in chemistry along with Sir John Kendrew.
Hb is an iron-containing oxygen-transport metalloprotein found majorly in the RBCs of all vertebrates except in the fish family Channichthyidae as well as in some invertebrates. The main function of Hb in mammals is to transport O2 from the lungs to various tissues of the body, but it is also known to interact with three other gases such as CO2, CO, and NO.
Hb is a tetramer made up of two α-globin chains and two β-globin chains which are encoded by two genes located on chromosomes 16 and 11, respectively. The β-globin gene cluster is packaged into inactive heterochromatin in nonerythroid cells, whereas the Hb-α genes are imbedded in open chromatin conformations in all cell types. Each of these chains has a heme moiety attached; thus individual chains can transport oxygen. Under physiological conditions it is involved in transport of oxygen from respiratory organs like lungs to various tissues through RBCs.