| SS4.02 Ecology and Physiology of Marine Organisms: Insights from Genes, Genomes, and Proteomes |
| Simoniello, C, , University of South Florida Coll. Mar. Sci., St. Petersburg, USA, simo@marine.usf.edu |
| Torres, J, J, University of South Florida Coll. Mar. Sci, St. Petersburg, USA, jtorres@marine.usf.edu |
| Somero, G, N, Stanford Univ. Hopkins Marine Station, Pacific Grove, USA, somero@leland.stanford.edu |
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| KINETIC PROPERTIES AND THERMAL STABILITIES OF A4_LACTATE DEHYDROGENASES OF MESOPELAGIC FISHES EVOLVED TO DIFFERENT THERMAL GRADIENTS |
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| Kinetic properties of the muscle-type intermediary metabolic enzyme lactate dehydrogenase (A4-LDH, EC 1.1.1.27, NAD+:lactate oxidoreductase)were positively correlated with the upper environmental temperature that mesopelagic fishes experience and negatively correlated with species' depth of occurrence. Reduced A4-LDH activity and catalytic rate constants (kcat) in deep-living species are patterns consistent with the greater thermal stability exhibited by their enzymes. Indices of binding affinity between enzyme and ligand, rates of enzyme performance and thermal stability all suggest that strong vertical migrators are more thermotolerant than asynchronous and non-migrating species. Turnover rates of the A4-LDH from mesopelagic fishes were approximately one-third the rate of those reported for shallow-living fishes experiencing similar habitat temperatures. The inefficient enzymes of mesopelagic fishes may be one factor of importance in establishing the upper limits of their distribution. |
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