[Changes in subunit composition of lactate dehydrogenase at low temperatures].

Hybridization of M4- and H4-isoenzymes of lactate dehydrogenase in saline medium was studied during slow freezing down to -9.5; -23 and -30 degrees C. It is established that appearances of the enzyme hybrid forms is associated with free water freezing out and with an increase in the concentration of salts in the solution. No hybridization was observed under fast cooling of the enzyme down to -196 degrees C, under exposition in the concentrated solution of chloride and sodium phosphate without freezing and with freezing in deionized water. The mechanism of low-temperature hybridization of lactate dehydrogenase, based on concentration effects of salts which favour dissociation of a protein molecule into subunits, are under discussion. An assumption is advanced on an intensification of intermolecular interactions in liquid microphases of the frozen solution as a possible reason of the subunits recombination into hybrid isoenzymes.