The Effect of Hypothermia on Some Structural and Functional Characteristics of Lactate Dehydrogenase of the Rat Brain

Abstract

Abstract—We studied the activity and some physicochemical parameters of LDH in the rat brain under normal and hypothermic conditions. It was found that during hypothermia the activity of LDH in the rat brain increases, while this increase is less pronounced in an enzyme preparation purified from ballast proteins. A study of LDH self-fluorescence showed a decrease in the intensity of total fluorescence of LDH, in which the main contribution is made by tryptophan residues. Analysis of the second derivatives of the fluorescence spectra showed that hypothermia affects tryptophanyls, which are located on the periphery of the LDH molecule. Study of the binding kinetics of the fluorescent probe ANS with LDH showed the presence of at least two types of binding sites of the probe, which differ in polarity. Hypothermia leads to a decrease in the fluorescence intensity of the ANS, a decrease in the number of binding sites, an increase in the probe dissociation constants, and a shift in the inflection position on the graph of the temperature dependence of the ANS fluorescence to higher temperatures. The study of the content of sulfhydryl and carbonyl groups in the LDH molecule suggests that one of the causes of the changes in the activity and spectral characteristics of LDH in the brain of hypothermic rats is the modification of the enzyme by reactive oxygen species.