Protection ofAcholeplasma LaidlawiiB by Superoxide Dismutase

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Abstract
Irradiation of Acholeplasma laidlawii B cells in air in the presence of superoxide dismutase produced a protective effect that had two components. The smaller component manifested itself immediately after the irradiation and depended on the buffer used. In Tris NaCl, pH 7·6, it amounted to an increase in D0 of 7·5 per cent or less; in phosphate glycerol buffer, pH 7·0, the increase amounted to 10·5–18·9 per cent, depending on the enzyme concentration. The larger component was elicited over a 4-hour period after irradiation and amounted to an increase in D0 of 17–52 per cent, depending on the enzyme concentration. A major portion of this component was also elicited by the enzyme when added to the cells 10 min after irradiation. Inactivated enzyme was generally ineffective. Mechanistically, these results require reactions involving the superoxide radical both during and after the irradiation and implicate sulphydryl oxidation as well as peroxidation of membrane phospholipids.