caa a22 4500 605514453 CHVBK 20210128100704.0 cr unu---uuuuu 210128e20150701xx s 000 0 eng 10.1007/s00360-015-0903-y doi (NATIONALLICENCE)springer-10.1007/s00360-015-0903-y Driedzic William Ocean Sciences Centre, Memorial University of Newfoundland, A1C 5S7, St. John's, NL, Canada aut Rainbow smelt: the unusual case of cryoprotection by sustained glycerol production in an aquatic animal [Elektronische Daten] [William Driedzic] Rainbow smelt flourish at −1.8°C, the freezing point of sea water. An antifreeze protein contributes to freeze point depression but, more importantly, cryoprotection is due to an elevation in osmotic pressure, by the accumulation of glycerol. The lower the water temperature, the higher theplasmaglycerol with levels recorded as high as 400mmoll−1. Glycerol freely diffuses out in direct relation to the glycerol concentration and fish may lose as much as 15% of their glycerol reserve per day. Glycerol levels decrease from a maximum in February/March while water temperature is still sub-zero. The decrease in glycerol may respond to a photoperiod signal as opposed to initiation which is triggered by low temperature. The initial increase in glycerol level is supported by liver glycogen but high sustained glycerol level is dependent upon dietary carbohydrate and protein. The metabolic pathways leading to glycerol involve flux from glycogen/glucose to the level of dihydroxyacetone phosphate (DHAP) via the initial part of glycolysis and from amino acids via a truncated gluconeogenesis again to the level of DHAP. DHAP in turn is converted to glycerol 3-phosphate (G3P) and then directly to glycerol. The key to directing DHAP to G3P is a highly active glycerol 3-P dehydrogenase. G3P is converted directly to glycerol via G3P phosphatase, the rate-limiting step in the process. The transition to glycerol production is associated with increased activities of enzymes at key loci in the top part of glycogenolysis/glycolysis. Curtailment of the final section of glycolysis may reside at the level of pyruvate oxidation with an inactivation of pyruvate dehydrogenase (PDH) driven by increased levels of PDH kinase. Enzymes associated with amino acid trafficking are elevated as is the pivotal enzyme phosphoenolpyruvate carboxykinase. Springer-Verlag Berlin Heidelberg, 2015 Aquaglyceroporin nationallicence Freeze resistance nationallicence Glycerol nationallicence Glycerol 3-P dehydrogenase nationallicence Glycerol 3-P phosphatase nationallicence Phosphoenolpyruvate carboxykinase nationallicence AFP : Antifreeze protein nationallicence AAT : Alanine aminotransferase nationallicence AQP : Aquaporin nationallicence DHAP : Dihydroxyacetone phosphate nationallicence FAD : Flavin adenine nucleotide (oxidized) nationallicence FADH2 : Flavin adenine nucleotide (reduced) nationallicence FBPase : Fructose 1,6 bisphosphatase nationallicence GAPDH : Glyceraldehyde 3-phosphate dehydrogenase nationallicence GDH : Glutamate dehydrogenase nationallicence GK : Glycerol kinase nationallicence G3P : Glycerol 3-P nationallicence G3PDH : NAD+-dependent glycerol 3-P dehydrogenase nationallicence G3PPase : Glycerol 3-P phosphatase nationallicence LDH : Lactate dehydrogenase nationallicence OXA : Oxaloacetate nationallicence PDH : Pyruvate dehydrogenase nationallicence PEP : Phosphoenolpyruvate nationallicence PEPCK : Phosphoenolpyruvate carboxykinase nationallicence PFK : Phosphofructokinase nationallicence PK : Pyruvate kinase nationallicence TMAO : Trimethylamine oxide nationallicence Journal of Comparative Physiology B Springer Berlin Heidelberg 185/5(2015-07-01), 487-499 0174-1578 185:5<487 2015 185 360 https://doi.org/10.1007/s00360-015-0903-y text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 review-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00360-015-0903-y text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Driedzic William Ocean Sciences Centre, Memorial University of Newfoundland, A1C 5S7, St. John's, NL, Canada aut NATIONALLICENCE 773 0- Journal of Comparative Physiology B Springer Berlin Heidelberg 185/5(2015-07-01), 487-499 0174-1578 185:5<487 2015 185 360