US EPA

1580164 

Journal Article 

The Radiation-Induced Inactivation of Lysozyme 

Aldrich, JE; Cundall, RB 

1969 

Yes 

International Journal of Radiation Biology
ISSN: 0955-3002
EISSN: 1362-3095 

NIOSH/00177775 

16 

4 

343-358 

The mechanism of radiation induced inactivation of lysozyme was investigated. Aqueous solutions of lysozyme saturated with oxygen, nitrogen or nitrous-oxide, and ranging in pH from 2 to 11, were irradiated with gamma rays from a cobalt-60 source at a dose rate of 600 rads per minute. The degree of inactivation of lysozyme was determined. Changes in the ultraviolet and visible absorption spectra, tryptophan content and amino acid composition induced by irradiation were determined. The irradiated solutions also underwent gel filtration and ultracentrifugation analysis. Optical rotatory dispersion spectra were recorded. Radical scavenging experiments utilizing thiocyanate ions, thallous ions and t-butyl-alcohol (TBA) were conducted. Lysozyme activity decreased exponentially for solutions saturated with nitrogen and nitrous-oxide at all pH values. Lysozyme activity decreased exponentially in oxygen saturated solutions only after an initial lag period of low radiosensitivity. The radiosensitivity increased at both high and low pH. Irradiating lysozyme in the absence of oxygen increased absorption at 280 nanometers (nm), whereas absorption at 280nm was decreased by the presence of oxygen. Irradiation in the presence of oxygen caused the greatest loss of tryptophan content, followed by irradiation in the presence of nitrous-oxide and nitrogen in that order. Irradiation in the presence of oxygen produced three molecular weight fractions of 41000, 24000 and 14300 daltons (d). Irradiation in the absence of oxygen yielded only the 41000 and 14300d fractions. Decreases in lysozyme structure were paralleled by decreases in helical content of the enzyme structure. Thiocyanate and thallous ions had no effect on lysozyme inactivation. The rate of inactivation was reduced by TBA. The authors suggest that the radiation induced inactivation of lysozyme is largely due to reactions of hydroxyl radicals with tryptophan residues. 

DCN-165586; Radiation exposure; Aqueous solutions; In vitro studies; Ionizing radiation; Molecular structure; Amino acids; Oxidative processes; Absorption spectrophotometry