Assays for Detection of RNase A Superfamily Ribonucleases

Ribonuclease A (RNase A), isolated from bovine pancreas, maintains a well-deserved place in the history of modern biochemistry, as many of the earliest studies on amino-acid sequencing, protein crystallography, and protein folding were performed on this stable and abundant protein ( 1 ). The existence of what is currently known as the ribonuclease (RNase) A superfamily (proteins with specific elements of shared sequence despite >50% amino-acid sequence divergence) emerged in the mid 1980s. There are currently six known human members of this superfamily, including pancreatic ribonuclease (RNase 1), eosinophil-derived neurotoxin (RNase 2), eosinophil cationic protein (RNase 3), RNase 4, angiogenin (RNase 5), and RNase 6 ( 2 , 3 ). Although elevated levels of serum ribonuclease activity were once thought to be diagnostic of pancreatic cancer ( 4 ), subsequent work demonstrated that serum ribonuclease activity was most closely correlated with declining renal function regardless of the underlying disease process ( 4 , 6 ). While not diagnostic of any specific disease or condition, ribonuclease activity has been used as a marker for the presence and activation state of human eosinophilic leukocytes both in vitro ( 7 , 8 ) and in vivo ( 9 , 10 ). For example, Harrison and colleagues ( 9 ) demonstrated that eosinophils recruited into the lower airways in response to infection with respiratory syncytial virus were activated and degranulating, as demonstrated by the presence of immunoreactive and ribonucleo-lytically active eosinophil-derived neurotoxin (EDN/RNase 2) and eosinophil cationic protein (ECP/RNase 3). These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.