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First published online November 24, 2003
Journal of Experimental Biology 207, 95-112 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00708
Effects of temperature acclimation on lactate dehydrogenase of cod (Gadus morhua): genetic, kinetic and thermodynamic aspects
1 Department of Biology, University of Antwerp, Groenenborgerlaan 171,
B-2020 Antwerp, Belgium
2 Department of Fisheries and Marine Biology, University of Bergen, PO Box
7800, N-5020 Bergen, Norway
3 Marine Biology/Ecological Physiology, Alfred-Wegener-Institute, Postfach
12 01 61, Columbusstrasse, D-27568 Bremerhaven, Germany
* Author for correspondence at present address: International University of Bremen, School of Engineering and Science, PO Box 750561, D-28725 Bremen, Germany (e-mail: m.zakhartsev{at}iu-bremen.de)
Accepted 8 September 2003
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
(
,
,
Vmax) or thermodynamic (Ea,
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 (G) 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
() 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
() 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
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.
Key words: allozyme, Arrhenius activation energy, fish, Gadus morhua, glycolysis, isozyme, kinetics, lactate dehydrogenase, LDH, liver, metabolic compensation, muscle, temperature acclimation
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