Phylogenic Study of Denaturation of Lactate Dehydrogenase Isoenzymes from Different Species by High and Low Temperature

We studied the influence of storage at different temperatures on lactate dehydrogenase (EC 1.1.1.27; LD) isoenzymes from different tissues and different species, and analysed biochemical and biophysical mechanisms of denaturation during storage. Isoenzymes obtained from tissue extracts of mammals, poultry, reptiles, amphibians and fish were shown to have their own denaturation ranges at low temperatures by post-treatment assays and transition temperature analysis. These ranges were between − 10 and − 20°C for most vertebrate LD isoenzymes. Circular dichroism analysis indicated that the denaturation of LD isoenzymes was probably caused by a change in the hydrophobic interactions in the molecule. At higher temperatures, LD-1 isoenzyme was more thermostable than LD-5 from the same animal species, except for rats, the LD-5 activity of which was more thermostable than the LD-1 activity. These findings indicate that variable effects of storage of samples and reference materials at low temperatures should be considered, and that it is necessary to establish LD isoenzyme standards for animal clinical laboratory investigations.