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

Abstract

The direct and indirect effects of 5 MeV electron beam irradiation in the range (0–400 Gy) at 20°C, 0°C, −3°C and −196°, as well as the influence of the aqueous suspending medium (ultrapure water 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, independently of the direct or indirect action of radiation. The temperature gradient used to lower the temperature of the samples to −196°C drastically influences the results. Freeze-thawing in two steps down to −196°C protects LDH to radiation, in the dose range used. The data obtained here inform on the high energy electrons effects on the enzymatic activity loss during irradiation and during thawing, when the subsequent growth of the water crystals [5] influences the three dimensional structure of the enzyme. 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 enzyme suspended in ultrapture water is reduced when compared to the enzyme suspended in bidistilled water, but compared to the D2O suspended enzyme is lightly increased.