Radiation inactivation analysis of enzymes. Effect of free radical scavengers on apparent target sizes
In most cases the apparent target size obtained by radiation inactivation analysis corresponds to the subunit size or to the size of a multimeric complex. In this report, we examined whether the larger than expected target sizes of some enzymes could be due to secondary effects of free radicals. To test this proposal we carried out radiation inactivation analysis on Escherichia coli DNA polymerase I, Torula yeast glucose-6-phosphate dehydrogenase, Chlorella vulgaris nitrate reductase, and chicken liver sulfite oxidase in the presence and absence of free radical scavengers (benzoic acid and mannitol). In the presence of free radical scavengers, inactivation curves are shifted toward higher radiation doses. Plots of scavenger concentration versus enzyme activity showed that the protective effect of benzoic acid reached a maximum at 25 mM then declined. Mannitol alone had little effect, but appeared to broaden the maximum protective range of benzoic acid relative to concentration. The apparent target size of the polymerase activity of DNA polymerase I in the presence of free radical scavengers was about 40% of that observed in the absence of these agents. This is considerably less than the minimum polypeptide size and may reflect the actual size of the polymerase functional domain. Similar effects, but of lesser magnitude, were observed for glucose-6-phosphate dehydrogenase, nitrate reductase, and sulfite oxidase. These results suggest that secondary damage due to free radicals generated in the local environment as a result of ionizing radiation can influence the apparent target size obtained by this method.
- Research Organization:
- Univ. of South Florida, Tampa
- OSTI ID:
- 6021494
- Journal Information:
- J. Biol. Chem.; (United States), Vol. 262:20
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
DNA POLYMERASES
CHEMICAL RADIATION EFFECTS
OXIDOREDUCTASES
RADICALS
BIOCHEMICAL REACTION KINETICS
BENZOIC ACID
CHICKENS
CHLORELLA
ESCHERICHIA COLI
IONIZING RADIATIONS
LIVER
YEASTS
ALGAE
ANIMALS
BACTERIA
BIRDS
BODY
CARBOXYLIC ACIDS
CHEMISTRY
DIGESTIVE SYSTEM
ENZYMES
FOWL
FUNGI
GLANDS
KINETICS
MICROORGANISMS
MONOCARBOXYLIC ACIDS
NUCLEOTIDYLTRANSFERASES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
PHOSPHORUS-GROUP TRANSFERASES
PLANTS
POLYMERASES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
REACTION KINETICS
TRANSFERASES
UNICELLULAR ALGAE
VERTEBRATES
560120* - Radiation Effects on Biochemicals
Cells
& Tissue Culture