(full paper is archived in the Miller Library)
Title: Temperature adaptation in elasmobranch lactate dehydrogenase-A (A4-LDH) ortholog structure
Student Author(s): Peace, Ali
Faculty Advisor(s): Somero, George
Location: Final Papers Biology 175H
Date: June 1998
Abstract: Thermal adaptation at the biochemical level has been demonstrated in previous studies of bony fishes and other vertebrates. One criterion that has been used to assess the possible presence of thermal adaptation is the Michaelis-Menten constant, or Km. Km has been shown to be conserved among teleosts and some other vertebrates within their physiological temperature ranges. One possible mechanism by which homologous proteins may conserve Km at extreme temperatures is by changes in primary structure. The relationship between temperature adaptation and changes in primary structure has been explored in teleosts, but has yet to be studied in elasmobranchs. In this study, the variation of pyruvate Km with temperature and the deduced amino acid sequences of four elasmobranch A4-LDH orthologs were compared. Both the subtropical and the cold temperate species of sharks were found to display conservation of pyruvate Km over physiological temperature ranges, while the subtropical and the antarctic species of rays did not. The deduced amino acid sequences of the shark enzymes exhibited different regions of variability than the LDH's of teleosts previously studied, while the sequences of the ray enzymes exhibited similar regions of variability to those of teleost orthologs. It was concluded that there may a limited number of sites at which temperature adaptation in A4-LDH occurs, and that even closely related organisms do not necessarily use the same sequence changes to adapt to extreme temperatures.