The amino acid sequence and disulfide bridges of bovine plasma derived 
angiogenin were determined by sequencer analysis of the intact protein and 
fragments derived by enzymatic and chemical digestion. Bovine angiogenin is a 
single-chain protein of 125 amino acids; it contains six cysteines and has a 
calculated molecular weight of 14,595. In contrast to the human protein its 
amino terminus is unblocked. It has the following sequence: 
H2N-Ala1-Gln-Asp-Asp-Tyr-Arg-Tyr-Ile-His-Phe10-Leu-Thr-Gln-His-Tyr -Asp-Ala-Lys- 
Pro-Lys20-Gly-Arg-Asn-Asp-Glu-Tyr-Cys-Phe-Asn-Met30-Met-Lys- Asn-Arg-Arg-Leu-Thr 
- Arg-Pro-Cys40-Lys-Asp-Arg-Asn-Thr-Phe-Ile-His-Gly-Asn50-Lys- 
Asn-Asp-Ile-Lys-Ala - 
Ile-Cys-Glu-Asp60-Arg-Asn-Gly-Gln-Pro-Tyr-Arg-Gly-Asp-Leu70- Arg-Ile-Ser-Lys-Ser 
- Glu-Phe-Gln-Ile-Thr80-Ile-Cys-Lys-His-Lys-Gly-Ser-Ser-Arg90- 
Pro-Pro-Cys-Arg-Tyr - 
Gly-Ala-Thr-Glu-Asp100-Ser-Arg-Val-Ile-Val-Val-Gly-Cys-Glu-Asn1 10-Gly-Leu-Pro- 
Val-His-Phe-Asp-Glu-Ser-Phe120-Ile-Thr-Pro-Arg-His-OH. Disulfide bonds link 
Cys(27)-Cys(82), Cys(40)-Cys(93), and Cys(58)-Cys(108). Bovine angiogenin is 64% 
identical with human angiogenin; like the human protein, it is homologous to the 
pancreatic ribonucleases, with conservation of active site residues. Two 
regions, 6-22 and 65-75, are highly conserved between the angiogenins but are 
significantly different from those of the ribonucleases, suggesting a possible 
role in the molecules' biological activity.