Abstract
Inhibitor of neutral ribonucleases (RNase inhibitor) is known to occur in a variety of animal tissues.However, a homogeneous RNase inhibitor has only been obtained from human placenta by Blackburn et al.(J.Biol.Chem., 252, 5904, 1977), and its molecular characteristics and physiological significance are still obscure.We attempted to purify a RNase inhibitor from bullfrog muscle, since we found that the bullfrog muscle contained a RNase inhibitor existing in two forms, a complex bound with RNase and a free form.
The procedure given for purification of the RNase inhibitor allowed homogeneous sample to be obtained in sufficient quantities for studies of the protein.The final preparation had a specific activity of 17, 064 units per mg.
The RNase inhibitor from bullfrog muscle is a protein of molecular weight 90, 000, it forms a1: 1 complex with a bullfrog liver RNase and is noncompetitive inhibitor of the bullfrog enzyme with a Ki of 0.7 to 1.0×10-9M.
The inhibitor is irreversibly inactivated by p-chloromercuribenzoate.The complex of the inhibitor and the bullfrog liver RNase dissociates into active RNase and inactive inhibitor in the presence of p-chloromercuribenzoate, whereas into active RNase and active inhibitor at a high concentration of sodium chloride.
