High energy electron beam inactivation of lactate dehydrogenase suspended in different aqueous media

The direct and indirect effects of 5 MeV electron beam irradiation in the r ange (0-400 Gy) at 20 degrees C, 0 degrees C, -3 degrees C and -196 degrees , as well as the influence of the aqueous suspending medium (ultrapure wate r and heavy water) on the total enzymatic activity of lactate dehydrogenase (LDH) have been studied. Our results showed an exponential decrease on the enzymatic activity of irradiated LDH, at all irradiation temperatures, ind ependently of the direct or indirect action of radiation. The temperature g radient used to lower the temperature of the samples to -196 degrees C dras tically influences the results. Freeze-thawing in two steps down to -196 de grees C protects LDH to radiation, in the dose range used. The data obtaine d here inform on the high energy electrons effects on the enzymatic activit y loss during irradiation and during thawing, when the subsequent growth of the water crystals [5] influences the three dimensional structure of the e nzyme. A 99.98% concentration of D2O in the suspending medium of the enzyme decreases the global enzymatic activity, but reduces the rate of radiation inactivation of the enzyme. The rate of radiation: inactivation of the enz yme suspended in ultrapure water is reduced when compared to the enzyme sus pended in bidistilled water, but compared to the D2O suspended enzyme is li ghtly increased.