The Effect of Ultraviolet Radiation Upon Enzymatic Activity and Viability of the Yeast Cell

Abstract

Suspensions of the cells of baker’s yeast were irradiated with ultraviolet light for sufficient times to produce populations of 75, 50, 30, and 5% viable cells. After washing and drying, various enzyme solutions were prepared from these cells. Enzymatic activities, on a nitrogen basis, were compared to those of solutions prepared from a nonirradiated population. At the 50% survival level, hexokinase, carboxylase, and zymase were inhibited to a degree roughly proportional to the viability. Carboxylase, and to a certain extent, hexokinase activity varied directly as the population viability. Catalase, alcohol dehydrogenase, and lactic dehydrogenase showed no diminution in activity even at the 5% survival level. These results suggest that although ultraviolet radiation may produce nuclear damage, the primary site of action may be certain enzymes of the cytoplasm.

The Action of Ultraviolet Radiation on Yeast Catalase

“…Cells were suspended in phosphate buffer, pH 7.2, throughout, except when otherwise specified. The lamp used in the irradiations was the same as that described by Aldous and Stewart (7) and by us (8); irradiations were carried out in the cold room or at room temperature, variations never exceeding I°C. during any run to be described.…”

Einflüsse äußerer Faktoren auf die Atmung

“…Bei Rickettsien fanden ALLEN und Mitarbeiter (1952) nach hohen UV-Dosen, die die Infektiösität der Zellen bis auf 0,001% herabsetzten, immer noch eine Atmungsgröße von 72% der unbestrahlten Kontrollen. Die Photosynthese von Scenedesmus und Chlorella ist gegen UV-Licht wesentlich empfindlicher als die Atmung (ARNOLD 1933). Ein ähnlicher Befund ergab sich auch bei Messung einzelner Fermentaktivitäten: Nach HoLT und Mitarbeiter (1951) ist die Hili-Reaktion isolierter Chloroplastenfragmente bereits stark geschädigt, bevor Polyphenol-oxydase, Cytochrom-oxydase oder Katalase eine merkliche Aktivitätsminderung zeigen.…”