Summary
Exposure of aqueous spinach ferredoxin solutions to X-rays results in a rapid and irreversible denaturation of the molecule. The denaturation is manifested by a decrease of the characteristic absorption of spinach ferredoxin at 320 and 416 nm, and by the concomitant liberation of ferric iron and hydrogen sulfide. The absorption decrease at 320 and 416 nm and the iron liberation are found to parallel the activity decrease in functioning as electron transfer factor in the noncyclic electron transport system in spinach chloroplasts.
X-ray inactivated spinach ferredoxin does not contain iron or free SH-groups, and can be regarded as anapo-form of the native protein. This X-ray-inactivated apoprotein, however, showed a higher molar extinction coefficient at 275 nm than the apoferredoxin, and was not reconstitutable.
Spinach ferredoxin was found to be even more radiosensitive than clostridial ferredoxin. AG- value of 1.25 for biological inactivation and iron liberation was found, as compared to aG- value of 0.8 for clostridial ferredoxin.
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Krasnobajew, V. X-ray inactivation studies of nonheme iron proteins the action of X-rays on Spinach ferredoxin in aqueous solutions. Biophysik 10, 213–220 (1973). https://doi.org/10.1007/BF01190580
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DOI: https://doi.org/10.1007/BF01190580