title: Ribonuclease inhibitor from bovine brain.
abstract: A ribonuclease inhibitor from bovine brain has been purified 27 000-fold by affinity chromatography on Sepharose-RNase A with an overall yield of 46% (ca. 0.4 mg/kg tissue). The purified inhibitor gives a single band by SDS-gel electrophoresis. By gel filtration the molecular weight is ca. 50 000; the molecular weight of the complex with bovine pancreatic RNase A is ca. 62 000, indicative of 1:1 binding on a molar basis. The inhibition of the action of RNase A on yeast RNA by the inhibitor is noncompetitive with a Ki of 7 x 10(-10) M. The protein is very similar in its properties, including amino acid composition, to the inhibitor previously isolated from human placenta. The amount of inhibitor per g of protein in bovine brain is about one-seventh of the value for human placenta. No difference was found in the distribution of inhibitor between white and gray matter; one-tenth of the inhibitor present is bound to a brain ribonuclease which is released in active form after reaction with p-hydroxymercuribenzoate. Essentially no free neutral ribonuclease activity could be detected in brain homogenates in the absence of p-hydroxymercuribenzoate.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D004586:Electrophoresis; D005260:Female; D006801:Humans; D008970:Molecular Weight; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D012260:Ribonucleases / Q000037:antagonists & inhibitors*
chemical_list: D000596:Amino Acids; D012260:Ribonucleases