MECHANISM OF ACTION OF IONIZING RADIATION ON RIBONUCLEASE (thesis)
The enzyme, bovine pancreatic ribonuclease, was chosen as the material for study in an attempt to establish a mechanism of the action of ionizing radiation on protein. The inactivation of ribonuclease cannot be accounted for by any single effect. At a high level of irradiation, 48 Mrad, roughly 15% of the molecules showed aggregation as determined by gel filtration, even after oxidation of the irradiated enzyme with performic acid. The same technique showed that about 5% of the total color developed by reaction with ninhydrin was due to fragments smaller than tripeptides. The amount of large fragments contributing to uv light absorption was estimated at 6% of the total absorbance at 280 m mu . These are clear evidences that chemical change took place in the molecules on irradiation. The binding of p-mercuribenzoate and Ag to the irradiated enzyme was observed. Whether that is due to their reaction with sulfhydryl groups produced by irradiation or due to any nonspecific reaction occurring at secondary binding sites on the enzyme is uncertain. Sulfhydryl groups may be considered to be generated with only 26% efficiency at the maximum. The loss of disulfide bonds of the enzyme was not detected which indicates that the sulfhydryl group may originate from a methionine residue. Conformational changes in the enzyme were reflected by a shift in the absorption spectrum and the appearance of minima in the difference spectrum reminiscent of the denaturation blue shift observed in other situations. The abnormal tyrosines, at least two of them, were also shown to be normalized. The enzyme became readily susceptible to tryptic digestlon suggesting an extensive loosening of its compact structure. These effects can be most likened to the phenomenon of denaturation known in protein chemistry. It is proposed that the disruption of hydrophobic bonds due to a radical or charge formation anywhere within the molecule can lead to a disorganization of the three-dimensional structure of the molecule which may then cause inactivation. The conformational change must be a consequence of a chemical modification at some point in the molecule. (auth)
- Research Organization:
- Yale Univ., New Haven
- NSA Number:
- NSA-17-040854
- OSTI ID:
- 4702330
- Report Number(s):
- TID-19494
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMINO ACIDS
ARYL RADICALS
BENZOIC ACID
CATTLE
CHEMICALS
CHEMISTRY
COLLOIDS
COLOR
DECOMPOSITION
EFFICIENCY
ENZYMES
FILTERS
FORMIC ACID
FREE RADICALS
GAMMA RADIATION
GLANDS
IONIZING RADIATIONS
IRRADIATION
ISOMERS
KETONES
MERCURY COMPOUNDS
METHIONINE
MOLECULES
NINHYDRIN
ORGANIC SULFUR COMPOUNDS
OXIDATION
PANCREAS
PEPTIDES
PROTEINS
RADIATION CHEMISTRY
RADIATION DOSES
RADIATIONS
REACTION KINETICS
RIBONUCLEIC ACID
RNA-ASE
SEPARATION PROCESSES
SILVER COMPOUNDS
SPECTRAL SHIFT
TRYPSIN
TYROSINE
ULTRAVIOLET RADIATION
X RADIATION