Abstract
Summary Polyacrylamide gel electrophoresis of potato tuber extracts allows the separation of five bands of ribonuclease activity. Deoxyribonuclease activity is confined to a single gel zone. All bands with ribonuclease activity appear in the electrophoretic pattern of supernatant of 100,000 g, which shows more than 90 per cent of total activity. However, the possibility of solubilization of particulate ribonuclease during tissue homogenization is not precluded. Aging of potato tuber disks causes a great increase in the activity of ribonuclease, while deoxyribonuclease activity is not significantly changed during the first 24 hr of incubation. During aging of disks the electrophoretic pattern of ribonuclease shows a considerable increase of activity in only one of the bands, with a simultaneous decrease in another. The remaining bands show no considerable variations. It has been possible to separate the enzyme corresponding to the band showing increased activity. The enzyme was isolated from aged tissue and partially purified by precipitation with ammonium sulfate, dialysis and Sephadex chromatography. It is a ribonuclease with pH optimum of 5.5, the activity of which is neither affected by Ca 2+ nor Mg 2+ ions, nor by ethylene diamine tetraacetate. This ribonuclease has no phosphodiesterase activity and is inactive against native or denatured DNA.
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