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).