Effects of radiation on frozen lactate dehydrogenase

Results concerning the influence of 6-MeV electron beam irradiation, of 1.3 5-GHz, 565-W microwaves, and of the combined electron and microwave irradia tion, at -21 degreesC and -196 degreesC, on lactate dehydrogenase activity are presented, The microwave-irradiated samples exhibited a non-linear beha viour (successive activation and inactivation of the enzyme molecules), sug gesting the major influence of the non-thermal component of microwave radia tion. The combined electron and microwave irradiation led to a decrease of activity similar to the one caused by electron beam irradiation, which seem ed to prove that microwave influence was insignificant in the dose, power a nd time ranges used. The radiation target analysis of the enzymatic decreas e due to electron irradiation indicated a very large aggregation of the enz yme molecules. Our data suggest that radiation target analysis is not suita ble to measure the molecular mass of lactate dehydrogenase, when frozen enz yme suspensions are irradiated. The D2O-protecred enzyme, when exposed to e lectron irradiation, showed an even larger aggregation according to radiati on target analysis, while the microwave irradiation of the protected enzyme led to a similar, though lesser, non-linear behaviour of the frozen enzyme molecules. (C) 2001 Elsevier Science B.V. All rights reserved.