Angiogenin (Ang) is a small polypeptide that is implicated in angiogenesis (formation of new blood vessels) in tumor growth . However, angiogenin is unique among the many proteins that are involved in angiogenesis in that it is also an enzyme with an amino acid sequence 33% identical to that of bovine pancreatic ribonuclease (RNase) A).

Moreover, although Ang has the same general catalytic properties as RNase A - it cleaves preferentially on the 3' side of pyrimidines and follows a transphosphorylation/hydrolysis mechanism - its activity differs markedly both in magnitude and in specificity.Although angiogenin contains counterparts for the key catalytic residues of bovine pancreatic RNase A, it cleaves standard RNase substrates 105 - 106 times less efficiently than does RNase A.