The Presence of a Ribonuclease of High Molecular Weight in Sugar Beet Storage Tissue

Soluble ribonuckasie activity in sliced root tissue or sugar beet (Beta vulgaris) decreased to 30% of initial levels during the first 15 hours of aeration in sterile phosphate buffer. Activity increased with continued aeration reaching a maximum at 30 hours (85% of initial levels). Ribonuclease activity was isolated from unaerated tissue and partially purified by precipitation with acid and ammonium sulfate and by Sephadex chromatography. Enzyme activity was linear with respect to enzyme and substrate concentrations. The enzyme exhibited a substrate preference for RNA with no activity in the presence of native or denatured DNA. Elution of the enzyme from a Sephadex G-150 column indicated a molecular weight of 155,000. This uniquely large ribonuclease had no phosphodiesterase activity, was unaffected by ethylenediamine tetraacetate, and was inhibited by increasing Nig²⁺ concentrations.