Lactate dehydrogenase from the Antarctic eelpout, Lycodichthys dearborni

Abstract

As part of our studies to examine the molecular basis of cold-adaptation, we have determined the kinetic properties, thermal stability and deduced amino acid sequence of the enzyme lactate dehydrogenase (LDH) from an Antarctic zoarcid fish, Lycodichthys dearborni. Unlike Antarctic notothenioid fish which are endemic to the Southern Ocean, zoarcid fish are cosmopolitan and have a substantially longer evolutionary history as a sub-order. The A4-LDH isoform was isolated and purified from the white muscle of L. dearborni. The kinetic parameters KmPYR and kcat were determined at temperatures from 0 to 25°C. KmPYR was substantially higher at low temperatures than those from Antarctic and temperate notothenioid fish, whereas kcat at these temperatures was essentially the same as those of the other fish LDH in this study. The sequence of L. dearborni A4-LDH was determined from cDNA derived from white muscle RNA and found to be similar to, but distinct from, the A4-LDH sequences of Antarctic notothenioid fish. Molecular modelling based on the structure of the A4-LDH from Pagothenia borchgrevinki suggested that three conservative amino acid changes within the core of the protein that are not directly part of the active site but which might nonetheless influence the active site, may be important in cold-adaptation in L. dearborni A4-LDH, and that several other changes on the surface of the protein might also play a role in cold-adaptation.