Lactate dehydrogenase isozymes of the flatfish, Pleuronectiformes: kinetic, molecular and immunochemical analysis

Anoxia- and hypoxia-induced expression of LDH-A* in the Amazon Oscar, Astronotus crassipinis

Adaptation or acclimation to hypoxia occurs via the modulation of physiologically relevant genes, such as erythropoietin, transferrin, vascular endothelial growth factor, phosphofructokinase and lactate dehydrogenase A. In the present study, we have cloned, sequenced and examined the modulation of the LDH-A gene after an Amazonian fish species, Astronotus crassipinis (the Oscar), was exposed to hypoxia and anoxia. In earlier studies, we have discovered that adults of this species are extremely tolerant to hypoxia and anoxia, while the juveniles are less tolerant. Exposure of juveniles to acute hypoxia and anoxia resulted in increased LDH-A gene expression in skeletal and cardiac muscles. When exposed to graded hypoxia juveniles show decreased LDH-A expression. In adults, the levels of LDH-A mRNA did not increase in hypoxic or anoxic conditions. Our results demonstrate that, when given time for acclimation, fish at different life-stages are able to respond differently to survive hypoxic episodes.

Lactate dehydrogenase in teleosts. The role of LDH-C4 isozyme

1. Lactate dehydrogenase (LDH) occupies an important position in cell metabolism. 2. Teleosts possess at least three genetic loci coding for lactate dehydrogenase subunits, Ldh-A, Ldh-B and Ldh-c. LDH exists in most tissues in several isozymic forms. 3. The isozyme LDH-C4 is synthesized predominantly in regions of the nervous system concerned with the eye.

Antisera probes to an atypical pseudocholinesterase from surgeonfish reveal immunochemical variability and tissue-specific molecular polymorphism

Polyclonal antisera were raised in rabbits against the purified sialated, presumed-globular tetrameric pseudocholinesterase (pseudo-ChE) from surgeonfish (Leibel: Journal of Experimental Zoology 1988b) and against commercially obtained Electrophorus electroplax AChE. The resulting antisera probes were absolutely specific for their respective antigens and failed to titrate ChE activities heterologously. However, each antisera probe did crossreact with its other respective globular and asymmetric aggregational isozymes. The resultant specific probes were then used to examine interspecific evolutionary conservation of the two ChE activities and, in conjunction with velocity sedimentation analysis and differential paraoxon inhibition, the tissue distribution and molecular polymorphism of these same two enzyme systems in surgeonfish. These experiments suggest the tight evolutionary conservation of AChE in contrast to the apparent high variability of pseudo-ChE amongst the wide range of teleost fishes tested. The native atypical pseudo-ChE was shown to exist, like AChE, as a series of sialated and asialated globular and asymmetric aggregational isozymes whose relative distribution exhibits marked tissue specificity. The extremely high levels of pseudo-ChE characteristic of white skeletal (epaxial) muscle, in particular, was conspicuous, and its occurrence in the sarcolemma is discussed in the context of its possible function and in relation to the apparent lack of evolutionary conservation amongst marine teleosts.

An apparent progressive and recurrent evolutionary restriction in tissue expression of a gene, the lactate dehydrogenase-C gene, within a family of bony fish (Salmoniformes: Umbridae)

Unexpectedly large differences in the tissue patterns of lactate dehydrogenase-C (Ldh-C) gene regulation were observed among species of fish within the family Umbridae (Salmoniformes). Normally, all the species within a family or order of advanced fishes exhibit the same, tissue-restricted pattern of L-lactate dehydrogenase C4 isozyme synthesis--either eye- or liver-restricted expression, but not both. However, within the Umbridae the more anciently derived species had a more generalized (primitive) tissue expression, whereas the more recently derived species had a more tissue-restricted expression, predominating in the eye. Given the relative divergence times among the species estimated by genetic distance (using 51 protein-coding loci), divergence from the presumed primitive expression of the Ldh-C gene appears to have been proceeding more rapidly in some species lineages than others. This narrowing of Ldh-C gene tissue regulatory specificity within the family Umbridae is similar to the general trend observed over much greater evolutionary times within the class of bony fishes. The results support the hypothesis of repeated evolutionary canalizations of Ldh-C gene regulation from the generalized tissue expression in more primitive species to a predictable tissue-restricted expression (in either eye or liver) in advanced species. Furthermore, in the Umbridae, this progressive restriction of tissue expression of isozymes has taken place during the evolution of both the Ldh-C and Ldh-B genes. These evolutionary trends in the regulation of isozyme-locus tissue expression in the bony fishes are consistent with either an intrinsically conditioned trend of change in gene regulation or with a response to natural selection.

Purification and properties of a C-type isozyme of lactate dehydrogenase from the liver of the Atlantic cod (Gadus morhua)

A C-type lactate dehydrogenase isozyme has been purified to homogeneity from the liver of the Atlantic cod. The enzyme consists of four identical subunits each with a mol. wt of 35,000. Optimum concentrations, Kms, and relative activities were determined for various substrates along with the optimum pH for the reaction with pyruvate and lactate. Glyoxalate, alpha-ketobutyrate, alpha-ketovalerate, and alpha-ketoglutarate were significantly reduced but branched chain alpha-ketoacids were not utilised as substrates. Substrate inhibition was observed for both lactate and pyruvate as is generally found for B-type lactate dehydrogenase isozymes but the lactate optimum concentration and Km more closely resemble the A-type lactate dehydrogenases.

Lactate dehydrogenase isozymes and allozymes of the nine-spined stickleback Pungitius pungitius (L.) (Osteichthyes: Gasterosteidae)

Zymograms indicate the existence of three loci coding for lactate dehydrogenase in the nine-spined stickleback Pungitius pungitius. The skeletal muscle locus is polymorphic for two codominant alleles: Ldh-A(100). and Ldh-A(140). Differences in allele frequencies among nine samples, obtained from eight geographically isolated populations, proved not significant in 28/36 pairwise comparisons. The frequency of Ldh-A(100) varied from 0.426 to 0.715. Significant differences in apparent Km (pyruvate) values were found among the LDH-A allozymes suggesting a functional basis for the selective maintenance of this polymorphism.

Mouse lactate dehydrogenase (LDH) C4 (testis) is immunochemically cross-reactive with LDH A4 (muscle) and LDHB4 (heart)

It has been reported that lactate dehydrogenase (LDH) purified from testes (LDH C) of homotherms is not immunochemically cross-reactive with somatic forms of LDH purified from heart (LDH B) or muscle (LDH A). On the basis of this premise, LDH C has been considered for use as a contraceptive vaccine. Data presented here indicate that mouse antisera to either mouse or rat LDH C are cross-reactive with LDH A and B purified from muscle and heart tissues of mice. However, rabbit antisera to mouse LDH C are not cross-reactive with either mouse LDH A or B. Thus, the degree of cross-reactivity is dependent on the species from which the immunogen LDH is purified, the antisera are derived, and the LDH used in the assay is purified. The determination that LDH A, B, and C are immunochemically cross-reactive is of importance in evaluating LDH C as an immunogen in an immunologic approach to contraception.

Characterization of monoclonal antibodies to the sperm-specific lactate dehydrogenase isozyme

The isozyme of lactate dehydrogenase (LDH) that is specific to testes, designated LDH-C4, is the predominant LDH isozyme in mammalian spermatozoa. Four high-affinity monoclonal antibodies have been developed to murine LDH-C4. These antibodies were tested for crossreactivity with LDH-C4 from rat, hamster, rabbit, and human by competitive binding radioimmunoassays. Monoclonal antibodies RG-1 and RG-2 are specific for adjacent or partially overlapping epitopes. The other two monoclonal antibodies each recognize separate and distinct determinants. One of these, designated RG-4, recognizes a sequential determinant that is contained in the coenzyme binding loop, residues 101-115 of the C subunit. Furthermore, RG-4 shows reduced binding affinity for rat LDH-C4 which differs in amino acid sequence at residue 108 and 111 in this region of the molecule. RG-4 also has reduced affinity for LDH-C4 of other species, which is consistent with substitutions in the amino acid sequences of the coenzyme binding loop. These differences between C4 of closely related species is in contrast to the high degree of conservation of this sequence in the LDH-A4 and LDH-B4 isozymes. These results provide useful information regarding homologies among species of LDH-C4 as well as the evolution of this isozyme.

Regulation of the synthesis of lactate dehydrogenase-X during spermatogenesis in the mouse

Total mouse testis RNA directs the synthesis of the sperm-specific C subunit of lactate dehydrogenase-X (LDH-X) when translated in a cell-free system derived from rabbit reticulocytes. The newly synthesized C subunits were isolated by immunoprecipitation with antibody specific for this isozyme, and quantitated by electrophoresis on SDS polyacrylamide gels. The amount of radioactivity incorporated into the enzyme subunit was directly proportional to the amount of testis RNA added to the translational system, thereby providing a sensitive and reliable method for assessing relative LDH-X mRNA activity. A combination of sucrose gradient centrifugation and oligo(dT)-cellulose chromatography resulted in a 23-fold purification of LDH-X mRNA over total cytoplasmic testis RNA. Analysis of LDH-X mRNA activity in the developing testis indicated that the appearance of functional LDH-X mRNA activity coincides with the appearance of LDH-X catalytic activity at 14 d postpartum. Measurement of LDH-X mRNA levels in separated testis cell populations prepared by centrifugal elutriation demonstrated that LDH-X mRNA represents 0.17-0.18% of the total functional mRNA activity in fractions enriched in pachytene spermatocytes and round spermatids, but only 0.09-0.10% of the translation products of elongated spermatids.

Lactate dehydrogenases of Atlantic hagfish: physiological and evolutionary implications of a primitive heart isozyme

Isozymes of lactate dehydrogenase from heart and muscle of Atlantic hagfish show less functional divergence than those from other fishes and higher vertebrates. The enzyme from hagfish heart (B4) displays a higher Michaelis constant for pyruvate and lower substrate inhibition at moderate pyruvate concentrations than heart isozymes from other species. These properties support the hypothesis that the ancestral vertebrate lactate dehydrogenase was a muscle (A4)-type enzyme and also suggest a role for the B4 enzyme in the unusual physiology of hagfish cardiac tissue which functions under sustained hypoxic conditions.

Evolution of isozyme loci and their differential tissue expression. Creatine kinase as a model system

The phylogeny of the creatine kinase (CK, EC 2.7.3.2) isozyme loci and their differential tissue expressions were determined for representatives of 65 families of vertebrates, with emphasis on the fishes. The transition from the single creatine kinase locus, characteristic of certain echinoderms, to the two creatine kinase loci which are orthologous to those present in all vertebrates, occurred early in the chordate line. The majority of pre-teleostean fishes possesses only these two CK loci (A and C). These loci are relatively generalized in their tissue expressions which are variable among species of primitive fishes. The third and fourth creatine kinase loci (B and D) arose separately in the ancestors of the bony fishes and appear to be the result of regional genome duplications. Concomitant with the increase in the number of isozyme loci has been an increase in the specificity of their tissue expression. In the advanced teleost fishes the four CK loci are differentially expressed in a characteristic manner. The A2 isozyme predominates in skeletal muscle, the B2 isozyme in eye and brain, the C2 isozyme in stomach muscle, and the D2 isozyme is found exclusively in testis. We propose a phylogeny of the creatine kinase genes in the lower chordates based on the time of appearance of new CK loci, the sequence in which the loci achieve a tissue restricted expression, and the immunochemical relatedness of the orthologous and paralogous gene products.

Strain differences in the immune response of mice to homologous sperm-specific lactate dehydrogenase (LDH-C4)

The sperm-specific isozyme of murine lactate dehydrogenase (LDH-C4) was injected into female mice of various strains. Two regulatory phenotypes characterize the resultant immunity to LDH-C4: one is manifested by high, intermediate or low levels of response, the other by the immediate or delayed maturation of peak titer. The response of several strains can be classified as high (SWR, SJL, BABL/c, C3H/He) and intermediate to low (A, CBA, DBA/2, DBA/1, C57BL/6) according to the level of antibody production and cell mediated immunity. BALB/c, SJL and SWR strains are immediate responders while DBA/2 and C3H/He mice are clearly delayed responders. Maturation and magnitude of response do not appear to be related. Both the antibody and cell mediated responses are T-dependent, but are not obviously associated with Ig allotype or H-2 regulation.

An allelic variant of the sperm-specific lactate dehydrogenase C4 (LDH-X) isozyme in humans

An unusual pattern of LDH isozymes was observed by gel electrophoresis of an extract of a human testis. This isozyme composition is consistent with an allelic variant of Ldh-c.

Immunochemical specificity of lactate dehydrogenase-X

Sperm-producing testes of mammals and some birds contain a unique form of lactate dehydrogenase (EC 1.1.1.27) which is a tetramer composed of C subunits, rather than the A and B subunits of lactate dehydrogenase isozymes 1-5. Immunochemical evidence is presented which confirms the hypothesis that the C subunit is encoded in a separate gene from the A and B polypeptides. The evolutionary relationships of these genes are discussed.