Ribonuclease structure elucidation

Ribonucleases are a widely distributed family of en-zymes that hydrolyze RNA by cutting the P—O ester bond attached to a ribose 5 carbon (fig. 8.12). A good representative of the family is the pancreatic enzyme ribonuclease A (RNase A), which is specific for a pyrimidine base (uracil or cytosine) on the 3 side of the phosphate bond that is cleaved. When the amino acid sequence of bovine RNase A was determined in 1960 by Stanford Moore and William Stein, it was the first enzyme and only the second protein to be sequenced. RNase A thus played an important role in the development of ideas about enzymatic catalysis. It was one of the first enzymes to have its three-dimensional structure elucidated by x-ray diffraction and was also the first to be synthesized completely from its amino acids. The synthetic protein proved to be enzymatically indistinguishable from the native enzyme. 

The three-dimensional structure of many enzyme molecules, including hydrolytic enzymes such as lysozyme, chymotrypsin, ribonuclease, carboxypeptidase A, elastase, and papain, has been determined in recent years throu] the X-ray diffraction method, and the steric arrangement and function of amino acid residues at the active site has been elucidated (/). 

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