Properties of the muscle and heart lactate dehydrogenases of the New Zealand hagfish,Eptatretus cirrhatus: Functional and evolutionary implications

Environmentally low-temperature kinetic and thermodynamic study of lactate dehydrogenase from Atlantic cod (G. morhua) using a 96-well microplate technique

Analyses of temperature-dependent kinetic parameters in enzymes extracted from tissues of ectothermic animals are usually carried out within the range of physiological temperatures (0-40 degrees C). However, multisample spectrophotometers (so-called microplate readers) with efficient wide-range temperature control (including cooling) have previously been unavailable. This limits the statistical quality of the measurements. A temperature-controlled microplate was designed for a 96-well microplate reader to overcome this limitation. This so-called T-microplate is able to control assay temperature between the freezing point of a liquid sample and 60 degrees C with high stability and accuracy in any data acquisition mode. At 4 degrees C the accuracy of the temperature control was +/-0.1 degrees C and temperature homogeneity across the microplate was +/-0.3 degrees C. As examples, analyses of the temperature dependence of Michaelis-Menten (K'(PYR)(m) and substrate inhibition (K'(PYR)(si) constants for pyruvate, of the maximal rate of reaction (V'(max), of the apparent Arrhenius activation energy (E(A), and of the Gibbs free-energy change (deltaG) of lactate dehydrogenases from muscle of Atlantic cod Gadus morhua acclimated to 4 degrees C are described. The large dataset obtained allowed evaluation of a new mechanism of metabolic compensation in response to seasonal temperature change.

Effects of temperature acclimation on lactate dehydrogenase of cod(Gadus morhua): genetic, kinetic and thermodynamic aspects

The aim of this study was to determine the effects of seasonal temperature variation on the functional properties of lactate dehydrogenase (LDH) from white muscle and liver of Norwegian coastal cod (Gadus morhua) and the possible relevance of LDH allelic variability for thermal acclimation. Two groups of fishes were acclimated to 4°C or 12°C for one year. Polymorphism was observed in only one (Ldh-B) of the three Ldh loci expressed in cod liver and/or muscle. Isozyme expression remained unchanged regardless of acclimation temperature(TA). The products of locus Ldh-B comprise only 14–19% (depending on the tissue) of total LDH activities and,consequently, differences between phenotypes are negligible in terms of their effect on LDH total performance. No kinetic(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{m}}^{\mathrm{PYR}}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}, Vmax) or thermodynamic (Ea,Δ G) differences were found among Ldh-B phenotypes. Clear kinetic differences were observed between LDH isoforms in the two tissues. However, the Arrhenius activation energy (Ea) for pyruvate reduction was the same for both tissues (Ea=47 kJ mol–1) at TA=12°C. Factors TA, tissue and phenotype did not reveal a significant effect on the Gibbs free energy change (ΔG) of the reaction(55.5 kJ mol–1). However, at TA=4°C,the Ea was increased (Ea=53–56 kJ mol–1) and the temperature dependence of the constant of substrate inhibition for pyruvate(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}) decreased in both muscle and liver.

In conclusion, the strategies of LDH adjustment to seasonal temperature variations in cod involve changes in LDH concentration (quantitative),adjustment of thermodynamic (Ea) and kinetic(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}) properties of the LDH(modulative) but not the expression of alternative isoforms (qualitative). We assume that the observed increase in Ea and the decrease of temperature dependence of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document} at low TA is the result of structural changes of the LDH molecule(temperature-driven protein folding). We propose a new mechanism of metabolic compensation of seasonal temperature variations – cold acclimation results in changes in the kinetic and thermodynamic properties of LDH in a way that favours aerobic metabolism through reduction of the competition of LDH for pyruvate in normoxic conditions.

Lactate dehydrogenase from the northern krill Meganyctiphanes norvegica: comparison with LDH from the Antarctic krill Euphausia superba

Electrophoretic polymorphism of lactate dehydrogenase (LDH, EC 1.1.1.27) from abdominal muscle is reported in the northern krill Meganyctiphanes norvegica. In the population, from the Gullmarsfjord (west coast of Sweden), LDH was encoded for by two different Ldh-A* and -B* loci. The isoenzymes were named according to their electrophoretic mobilities. Ldh-A* locus was polymorphic. The allelic frequencies were a=0.99, a'=0.002, a"=0.004, a"'=0.004. The level of LDH polymorphism is low. Most individuals possess the same amount of two LDH homopolymers (LDH-A*(4) and LDH-B*(4)). The Meganyctiphanes norvegica LDH-A*(4) and LDH-B*(4) isoenzymes and the predominant LDH-A*(4) isoenzyme from Euphausia superba were purified to specific activities of 294, 306 and 464 micromol NADH min(-1) mg(-1), respectively. In both species the LDH isoenzymes were separated by chromatofocusing. All three isoenzymes are L-specific tetramers with molecular weight of approximately 160 kDa. Northern krill LDH-A*(4) has higher affinity for pyruvate and lactate and is more thermostable than LDH-B*(4). Both isoenzymes are inhibited significantly by high concentration of pyruvate but not lactate. Antarctic krill isoenzyme exhibits high substrate affinities, high NAD inhibition, high inhibition at 10 mM pyruvate, lack of lactate inhibition, and high heat stability and resembles northern krill LDH-A*(4) isoenzyme.