Immunochemical evidence that the single lactate dehydrogenase of lampreys is more similar to LDHB4 than to LDHA4 of hagfish

Comparative enzymology-new insights from studies of an "old" enzyme, lactate dehydrogenase

Comparative enzymology explores the molecular mechanisms that alter the properties of enzymes to best fit and adapt them to the biotic demands and abiotic stresses that affect the cellular environment in which these protein catalysts function. For many years, comparative enzymology was primarily concerned with analyzing enzyme functional properties (e.g. substrate affinities, allosteric effectors, responses to temperature or pH, stabilizers, denaturants, etc.) in order to determine how enzyme properties were optimized to function under changing conditions. More recently it became apparent that posttranslational modifications of enzymes play a huge role in metabolic regulation. At first, such modifications appeared to target just crucial regulatory enzymes but recent work is showing that many dehydrogenases are also targets of posttranslational modification leading to substantial changes in enzyme properties. The present article focuses in particular on lactate dehydrogenase (LDH) showing that stress-induced changes in enzyme properties can be linked with reversible posttranslational modifications; e.g. changes in the phosphorylation state of LDH occur in response to dehydration stress in frogs and anoxia exposure of turtles and snails. Furthermore, these studies show that LDH is also a target of other posttranslational modifications including acetylation, methylation and ubiquitination that change in response to anoxia or dehydration stress. Selected new methods for exploring posttranslational modifications of dehydrogenases are discussed and new challenges for the future of comparative enzymology are presented that will help to achieve a deeper understanding of biochemical adaptation through enzyme regulation.

Evolutionary implications of lactate dehydrogenases (LDHs) of hagfishes compared to lampreys: LDH cDNA sequences from Eptatretus burgeri, Paramyxine atami and Eptatretus okinoseanus

Heart muscles of hagfishes Paramyxine atami and Eptatretus okinoseanus express the B4 isozyme of lactate dehydrogenase [L-LDH: NAD oxidoreductase, EC 1.1.1.27] (LDH-B4) whereas their skeletal muscles express LDH-A4. To examine the relationship of hagfish LDHs to lamprey and other vertebrate LDHs, we determined the cDNA sequences of LDH-A from three hagfishes and compared them with previously published sequences. A phylogenic tree shows that hagfishes diverged just after lampreys. The deduced amino acid sequences showed ten regions common to all vertebrate LDHs examined, i.e., the active site, the pocket recognizing the substrate-coenzyme complex, part of a loop at the surface, and the substrate binding site. The cyclostomate-specific regions (S1, S2) were located in the neighborhood of the active site loop. Three regions, IGS1, IGS2 and IGS3, seem to have altered their structures during the differentiation of LDH isozymes, and the regions remain in LDH-B of vertebrates hitherto examined. IGS2 and IGS3, which are in the neighborhood of the active site, may regulate catalytic activity. There were differences in six amino acid residues (6, 10, 20, 156, 269, and 341) in LDHs of hagfishes. These differences might reflect the tolerance to high pressure and low temperature of LDHs from hagfishes at different habitat depths.

Effects of urea on M4-lactate dehydrogenase from elasmobranchs and urea-accumulating Australian desert frogs

We measured the effect of urea on M4-lactate dehydrogenase (M4-LDH) from elasmobranchs and Australian desert frogs (urea accumulators) and from two animals that do not accumulate urea, the axolotl and the rabbit. An analysis of the effect of urea on the Kd(NADH), V, V/K(m(prr)) and V/K(m(NADH)) shows that in all cases the major effect of urea was on the binding of pyruvate, which fits with data in the literature that show that urea acts as a competitive inhibitor of LDH. The characteristics of the elasmobranch enzymes are consistent with a proposed adaptation model, but the situation for the enzymes from the aestivating frogs is equivocal. Urea (400 mM) had less effect on the K(m(prr)) of M4-LDH from the urea accumulators than it did on the non-accumulators, suggesting a general adaptation and that the enzyme produced by the aestivating frogs (urea accumulators) is kinetically different from that of non-aestivating frogs (non-accumulators). A new approach is used to characterize the overall pattern of adaptation to urea. The pattern is similar in an enzyme from an elasmobranch and an aestivating frog despite the temporary presence of urea in the latter and the phylogenetic difference between these animals.

Sequence analysis of teleost retina-specific lactate dehydrogenase C: evolutionary implications for the vertebrate lactate dehydrogenase gene family

At least two gene duplication events have led to the three lactate dehydrogenase (LDH; EC 1.1.1.27) isozymes (LDH-A, LDH-B, and LDH-C) of chordates. The prevailing model for the evolution of the LDH loci involves duplication of a primordial LDH locus near the origin of vertebrates, giving rise to Ldh-A and Ldh-B. A third locus, designated Ldh-C, is expressed in the spermatocytes of mammals and a single family of birds and in the eye or liver tissues of teleost fishes. Ldh-C might have arisen independently in these taxa as duplications of either Ldh-A or Ldh-B. Several authors have challenged this traditional hypothesis on the basis of amino acid sequence and immunological similarity of the three LDH isozymes. They suggest that the primordial LDH gene was duplicated to form Ldh-C and a locus that later gave rise to Ldh-A and Ldh-B. We have differentiated between these hypotheses by determining the cDNA sequence of the retina-specific LDH-C from a teleost, Fundulus heteroclitus. On the basis of amino acid sequence similarity, we conclude that the LDH-C isozymes in fish and mammals are not orthologous but derive from independent gene duplications. Furthermore, our phylogenetic analyses support previous hypotheses that teleost Ldh-C is derived from a duplication of the Ldh-B locus.

Evolutionary implications of the cDNA sequence of the single lactate dehydrogenase of a lamprey

All vertebrates other than lampreys exhibit multiple loci encoding lactate dehydrogenase +ADL-LDH; (S)-lactate:NAD+ oxidoreductase, EC 1.1.1.27+BD. Of these loci, Ldh-A is expressed predominantly in muscle, Ldh-B is expressed predominantly in heart, and Ldh-C (where present) exhibits different tissue-restricted patterns of expression depending on the taxon. To examine the relationship of the single LDH of lampreys to other vertebrate LDHs, we have determined the cDNA sequence of the LDH of the sea lamprey Petromyzon marinus and compared it to previously published sequences from bacteria, plants, and vertebrates. The lamprey sequence exhibits a mixture of features of both LDH-A and LDH-B at the amino acid level that may account for its intermediate kinetic properties. Both distance and maximum parsimony analyses strongly reject a relationship of lamprey LDH with mammalian LDH-C but do not significantly distinguish among remaining alternative phylogenetic hypotheses. Evolutionary parsimony analyses suggest that the lamprey LDH is related to Ldh-A and that the single locus condition has arisen as a result of the loss of Ldh-B (prior to the appearance of Ldh-C). The collection of LDH sequences for further studies of the evolution of the vertebrate LDH gene family will be facilitated by the PCR approach that we have used to obtain the lamprey sequence.

Some aspects of isozymes of lactate dehydrogenase, malate dehydrogenase and glucosephosphate isomerase in fish

1. The present paper reports some aspects of the isozymes of LDH, MDH and GPI in fish. 2. In Petromyzontiformes LDH is encoded by a single Ldh-A gene locus. In Myxiniformes and in most vertebrates LDH is encoded by two gene loci, A and B. A third Ldh-C locus is characteristic of the bony fishes Actinopterygii. 3. In fish the MDH isozymes are generally encoded by three gene loci Mdh-M, Mdh-A and Mdh-B. 4. In most diploid bony fish the GPI is controlled by two independent gene loci Gpi-A and Gpi-B. 5. The relationships of isozymes with evolution of vertebrates, tissual specificity, ontogenetic changes, with physiological and metabolic roles are discussed.

Coexpression of distinct eye- and liver-specific LDH isozymes in cichlid fish

In a recent electrophoretic survey of lactate dehydrogenase (LDH) in neotropical cichlid fishes (Perciformes, Cichlidae) we have discovered several species in which a cathodal liver-specific isozyme is expressed along with the highly-anodal eye-specific isozyme (LDH-C4) typically encountered in perciform fishes. We believe this fourth, liver-specific LDH isozyme to be real and not artifactual since homogenization of fresh liver from one of these species, the Basketmouth cichlid (Acaronia nassa), in either of two nondenaturing detergents or in the presence of the protease inhibitor phenylmethylsulfonylfluoride affects neither the presence nor mobility of this cathodal band. Moreover, it continues to be expressed in the captively bred F1 of these same wild fish. The discovery of several fish species, like the Basketmouth, in which biochemically distinct eye- and liver-specific LDH isozymes are coexpressed, is discussed in light of the currently accepted hypothesis that these two isozymes are encoded by a single locus (LDH-C) which has undergone divergent tissue expression in several other major teleost groups. Preliminary characterization of the liver-specific isozyme relative to the eye-specific LDH-C4 in the Basketmouth cichlid with respect to thermolability and NADH-induced binding to oxamate-sepharose columns suggests that the eye- and liver-specific LDH isozymes are biochemically quite distinct in this fish and that they are probably encoded by two distinct loci.