Ribonuclease and Ribonuclease-Inhibitors Among Higher Plants

1) Aqueous extracts prepared from 41 common plants were tested for ribonuclease activity and for capacity to inhibit pancreatic ribonuclease. Extracts of 5 plants (Phlox sp., Lathyrus sp., Asclepias syriaca, Allium sp. and Yucca filamentosa) were found capable of degrading ribonucleic acid, and these plants appear to constitute new sources of ribonuclease. It is known that similar enzymes are present in wheat(6), in sprouting soy beans(7) and in various other types of germinating seeds (8-10), but there appears to be little information concerning the occurrence and distribution of ribonuclease in the plant kingdom in general. 2) A new, naturally occurring inhibitor of pancreatic ribonuclease is shown to be present in lilac leaves. It is a thermostable dialyzable substance of unknown identity. An apparently similar substance is present also in privet leaves. The agent present in lilac inhibits not only pancreatic ribonuclease but also Asclepias ribonuclease, and to a less extent Lathyrus ribonuclease. The specificity of the lilac inhibitor is compared with that of magnesium ion and heparin.