NONTHERMAL EFFECTS OF MICROWAVES ON PROTEINS - THERMOPHILIC ENZYMES AS MODEL SYSTEM

Two thermophilic and thermostable enzymes, isolated from Sulfolobus so lfataricus, S-adenosylhomocysteine hydrolase and 5'-methylthioadenosin e phosphorylase, were exposed to 10.4 GHz microwave radiation in order to discriminate between thermal and non-thermal microwave effects. Th e exposure causes a non-thermal, irreversible and time-dependent inact ivation of both enzymes; the inactivation rate is related to the energ y absorbed and is independent of the enzyme concentration. The influen ce of salts on enzyme inactivation has also been investigated. Conform ational changes of S-adenosylhomocysteine hydrolase, detected by fluor escence and circular dichroism techniques, suggest that microwaves ind uce protein structural rearrangements not related to temperature.