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, thereby preventing protein formation and exerting a cytotoxic effect on tumor cells. This agent also activates caspase-9 in mitochondria, resulting in tumor cell apoptosis. (NCI04)