Isolation of bovine angiogenin using a placental ribonuclease inhibitor binding assay

Angiogenin, which induces the formation of new blood vessels, was isolated previously from two human sources--HT-29 tumor conditioned media and normal plasma. By use of a newly developed binding assay, a similar protein has now been purified from bovine plasma at levels of 30-80 micrograms/L. This protein has the structural, enzymatic, and biological characteristics expected for an angiogenin molecule. Its amino acid composition is similar to that of the human protein, and 22 of 31 residues in the amino-terminal sequences are identical, including a block of 11 consecutive residues. Like human angiogenin, the bovine protein binds placental ribonuclease inhibitor, is inactive toward conventional RNase A substrates, and displays selective ribonucleolytic activity toward some rRNAs. In addition, the bovine protein induces angiogenesis in vivo in the chick embryo chorioallantoic membrane assay at levels as low as 44 fmol per egg. Thus, angiogenin is present in bovine sera at levels similar to those observed in man, and its enzymatic and biological activities are identical with those of the human protein.