Criteria for Searching for Proteins with High Osmotic Activity in the Blood of Albumin-Free Teleost

The criteria for searching for proteins-substitutes for the osmotic function of serum albumin in the blood of albumin-free fish that have lost albumins during the evolutionary process have been developed: (1) high negative charge of the proteins-substitutes (q) as a measure of their high osmotic activity and/or (2) the ability to remodel with the formation of particles with high q. In albumin-free fish, these criteria are met by multiple serum α-globulins: α-antitrypsin (AIAT); heat acclimation protein Wap65 or hemopexin Hx; apolipoproteins A in high-density lipoproteins (HDL) content. Their status as factors with high osmotic activity comparable to mammalian albumins is confirmed by experimental data from various authors. Comparison of the organization of serum α-globulins in albumin-free fish and mammals with analbuminemia allowed us to identify strategies in fish (1) to enhance the negative charge of AIAT and Wap65, which is not typical for AIAT and Hx in humans, and (2) to the dominant content of HDL lipoproteins in the blood of fish, which, during remodeling in the experiment and , form particles with high q and high water-binding activity. The results obtained confirm the concept of the stability of the protein system of plasma in Vertebrata, capable of compensating for the functions of individual proteins lost during the evolutionary process and adapting to environmental conditions due to adaptive changes in the organization of own proteins, including by changing their surface charge, which affects osmotic activity.