Effects of radiation on frozen lactate dehydrogenase

Results concerning the influence of 6-MeV electron beam irradiation, of 2.45-GHz, 565-W microwaves, and of the combined electron and microwave irradiation, at -21 degrees C and -196 degrees C, on lactate dehydrogenase activity are presented. The microwave-irradiated samples exhibited a non-linear behaviour (successive activation and inactivation of the enzyme molecules), suggesting the major influence of the non-thermal component of microwave radiation. The combined electron and microwave irradiation led to a decrease of activity similar to the one caused by electron beam irradiation, which seemed to prove that microwave influence was insignificant in the dose, power and time ranges used. The radiation target analysis of the enzymatic decrease due to electron irradiation indicated a very large aggregation of the enzyme molecules. Our data suggest that radiation target analysis is not suitable to measure the molecular mass of lactate dehydrogenase, when frozen enzyme suspensions are irradiated. The D2O-protected enzyme, when exposed to electron irradiation, showed an even larger aggregation according to radiation target analysis, while the microwave irradiation of the protected enzyme led to a similar, though lesser, non-linear behaviour of the frozen enzyme molecules.