A Biological Assay for Ribonuclease with Sub-millimicrogram Sensitivity

Summary An ultra-sensitive method of assay for ribonuclease (RNase) has been devised using a biologically active ribonucleic acid (RNA) as its substrate. Infectious RNA isolated from foot-and-mouth disease virus was exposed to suitable dilutions of RNase, and the resulting loss in RNA infectivity was measured by plaque assay in calf-kidney cultures. Concentrations of enzyme as low as 0.1 mμg per ml were readily detected. The RNase level in sera from man and several animal species was determined by this method. Most sera contained 0.02 to 0.1 μg/ml of RNase, but guinea pig serum had a 20- to 30-fold higher content of this enzyme.