Angiogenin is a potent blood-vessel-inducing polypeptide with a molecular weight 
of 14,000 that has a unique ribonucleolytic activity. First isolated from the 
conditioned medium of tumour cells, angiogenin has since been purified from 
normal plasma, which suggested that its propensity to induce neovascularization 
should be strictly controlled. Modulation of that activity might involve 
interaction of angiogenin with cell-surface receptors and extracellular matrix 
of endothelial cells, tight-binding inhibition of both its ribonucleolytic 
activity and cell binding property by ribonuclease inhibitor, as well as the 
overall influence of divalent copper, a modulator of angiogenesis.