2008 Volume 2 Issue 1 Pages 54-60
Lactate dehydrogenase (L-lactate: NAD oxidoreductase, EC 1.1.1.27; LDH) is one of the important enzymes in the glycolytic reaction cascade for its metabolic significance in catalyzing the terminating step. Cell-free extracts able to catalyze the oxidation of lactate to pyruvate were first obtained in 1932 (Banga et al., 1932). Warburg and Christian (1936) later associated the reaction with NAD , and the enzyme was first purified from bovine heart muscle (Straub, 1940). Since then, LDH has been extensively studied in vertebrates, plants and bacteria (Loewus and Stafford, 1960; Dennis and Kaplan, 1960; Biellmann and Rosenheimer, 1973). The direction of the reversible reaction depends on tissue-specific physiological conditions, such as the NAD/NADH ratio and the oxygen partial pressure. In most vertebrates, the LDH molecule forms a tetrameric structure (Markert and Moller, 1959) and two separate loci which encode A and B subunits constructing 5 tetrameric isozymes have been found (Prochazka and Wachsmuth, 1972). In cyclostomata, E. japonica has been shown to have a single subunit, while hagfishes have 2 subunits, LDH-A and LDH-B. Thus, hagfish LDH-B is the most primitive LDH-B ever examined. To examine the relationship of hagfish LDHs to lampreys and other vertebrate LDHs, we determined the cDNA sequences of LDH-A from 3 hagfishes and compared them to previously published sequences. The effect of high hydrostatic pressure on LDH activity was examined under pressures from 0.1 to 100 MPa. These results suggest that LDH-A4 of E. okinoseanus is more adapted to high-pressure conditions than others.
