Caption：Ribonuclease A (RNAse A) is a secreted enzyme that hydrolyzes RNA during digestion. This diagram utilizes the structure of the bovine (Ros taurus) protein. (a) Shown is a space-filling model of RNAse A with a bound substrate (black stick model.) (b) The same enzyme is shown with a ribbon model of the protein backbone. (c) This close-up view of the substrate binding site depict the substrate analog (5'-diphosphoadenosine- 3'-phosphate) in space-fill model. The side-chains of the amino acid residues in the active site are shown in ball-and-stick model while the remainder of the protein is represented in ribbon form. [PDB 1AFK]
Notes：The color coding on the ball-and-stick and spacefill models is blue=nitrogen, gray=carbon, red=oxygen, yellow=sulfur, purple=phosphorus. Hydrogens are not shown.