The isolation and properties of the enzyme uricase

Abstract

A method has been evolved whereby the enzyme uricase can be isolated from pig liver, and a preparation 500 - 700 times more active than the starting material has been obtained. The purest preparatlon has a specific activity of 85 - 90 μl. per mg . per min . compared with 0.12 - 0 .15 μ1. per mg . per min. for the dry liver powder used as starting material.The pure enzyme is a white protein, insoluble in water , almost insoluble in phosphate buffer pH 7.4 but soluble in alkaline solutions such as borate buffer pH 10 . Solutions of the enzyme are almost colourless . The enzyme contains 0 .15 - 0.20% iron , a mere trace of copper, no cobalt or manganese, and 14.4% of nitrogen .The activity of the enzyme is retained for several weeks when it is preserved in t he form of a solution in borate buffer at 0° but the free protein loses its activity more rapidly . The enzyme cannot be dried without great loss of activity.The velocity of the enzyme action is proportional to the oxygen pressure being only 7% as great in a mixture of 2% oxygen and 98% argon as in 100% oxygen. When argon is replaced by carbon monoxide no inhibition occurs .On the other hand the enzyme is completely inhibited by cyanides in a concentration as low as M/20,000.Inhibition by cyanide suggests that the enzyme is a heavy metal compound and the possibility exists that iron is the active group of the enzyme although thi s has not been conclusively proved.The iron appears to be tightly bound to the protein and all attempts to remove it have failed .