Lactate dehydrogenase isoenzymes expression in sticklebacks

Abstract

The lactate dehydrogenase (LDH, L-lactate, NAD + oxidoreductase, EC 1.1.1.27) is a tetrameric enzyme whose monomers are coded for by three independent loci: LdH-A, LdH-B; Ldh-C. The enzyme is a protein made up of different combinations of a small number of polypeptide chains which are products of these three loci. In most teleost fishes, the LDH-A 4 and LDH-B 4 isoenzymes are predominant in skeletal and heart muscles, respectively, while the LDH-C 4 isoenzyme occurs in a great many tissues in the primitive teleosts or its function is restricted to liver (many species in orders Cypriniformes and Gadiformes) and eye (the other teleosts). The LDH isoenzymes of two widely distributed species of sticklebacks, the threospine sticklebac ( Gasterosteus aculeatus) and the ninespeine stickleback ( Pungitius pungitius), were studied. It was demonstrated that LDH in these sticklebacks is under control of three independent loci—Ldh-A, Ldh-B and Ldh-C. There was no polymorphism detected in any of the loci from the threespine stickleback. Both kinds of heterotetramers, between A and C or B and C subunits, were formed in the threespine and ninespine sticklebacks. It was alos revealed that these two sticklebacks possess the same LDH isoenzyme in heart and skeletal muscles which was designated as LDH-A 4. The LDH-B 4 isoenzyme function was restricted to eye and brain tissues. The same LDH tissue distribution pattern is well known in species of the order Pleuronectiformes. Further detailed investigations on the other Gasterosteidae species and orders related to them should probably confirm if this unusual expression of the Ldh-B locus has the systematic value.