Hot mitochondria
Mitochondria in human cells warmed up to 50 degrees
Daria Spasskaya, N+1
The researchers measured the temperature of the working mitochondria and found that during cellular respiration, the organelle warms up to almost 50 degrees. In a paper published in the journal PLOS Biology (Chrétien et al., Mitochondria are physiologically maintained at close to 50 °C), the scientists also showed the thermal stability of enzymes associated with the mitochondrial membrane.
Mitochondria oxidize organic substances and store the released energy in the form of ATP, the universal "energy currency" of the cell, but most of the energy is dissipated into heat. Thermogenesis is also an important function of mitochondria – for example, brown fat cells, which are necessary to maintain body temperature for infants and animals during hibernation, contain a lot of mitochondria.
Complexes of enzymes are concentrated on the inner membrane of mitochondria, which ensure the oxidation of substrates, the formation of an electrochemical gradient on the membrane and, ultimately, the synthesis of ATP. These complexes form the so-called respiratory (electronic transport) chain.
Researchers from Using the thermosensitive fluorescent dye MitoThermo Yellow, the temperature of the mitochondria operating at full capacity in the HEK293 human cell culture and the primary culture of skin fibroblasts was measured at the University of Paris. It turned out that under physiological conditions, the organelle "warms up" by 7-12 degrees above the ambient temperature, which was 38 degrees Celsius. Thus, the physiological optimum of mitochondrial function is about 50 degrees.
The temperature of the organelles was indirectly determined by the fluorescence of the dye, which decreases linearly when heated. The researchers confirmed that warming up normally is associated with the work of the respiratory chain: substances suppressing its activity, such as cyanide and oligomycin, led to increased fluorescence of the dye. The additional expression of "thermogenesis proteins" in cells, for example UCP1, on the contrary, led to an even greater decrease in fluorescence, that is, heating of mitochondria.
Usually organisms cannot function for a long time at elevated temperatures due to the denaturation of enzymes at temperatures above 40 degrees. Nevertheless, there are many thermophilic organisms that live in an environment with temperatures up to 90 degrees Celsius. Thus, there are enzymes in nature, the optimum of which is shifted above 37 degrees. The authors measured the temperature optimum of several enzymes of the electron transport chain, in particular, cytochrome With reductases, and confirmed that it is equal to about 50 degrees, so warming up the mitochondria is quite possible without losing their activity.
The authors themselves claim that their discovery is quite surprising, and urge colleagues to check the conclusions of the work themselves. Although scientists have tried to check all the factors that could affect the "thermometer readings", perhaps something was still missed. Reviewer of the work Nick Lane generally argues that these figures should not be taken literally, since at the cellular level the very definition of temperature can change.
Despite the obvious need for mitochondria for the cell, their work is also associated with negative effects – in particular, the work of the respiratory chain leads to the formation of reactive oxygen species and oxidative stress. Scientists have shown that reducing the efficiency of mitochondria or even removing them from cells eliminates signs of aging. And in 2016, eukaryotic organisms were discovered in whose cells there are no mitochondria at all – these are protists from the Monocercomonoides group.
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