A natural homologue of ribonuclease A isolated from the eggs of the frog Rana pipiens. Ranpirnase primarily degrades cellular transfer RNA with a substrate specificity for uridine-guanidine base-pair sequences, resulting in inhibition of protein synthesis and cytotoxicity. This agent also activates caspase-9 in mitochondria, resulting in tumor cell apoptosis. orA substance being studied in the treatment of cancer. It is a type of ribonuclease enzyme. Also called Onconase.