Adenosine deaminase from human thyroid purification and some properties

Gel filtration of human thyroid extract with Sephadex G-200 revealed two molecular forms of adenosine deaminase differing in their molecular sizes. The smaller form of adenosine deaminase was purified over 120-fold by precipitation of the protein impurities at pH5.6 and chromatography on DEAE-Sephadex A-50, Sephadex G-100 and adenosine-Sepharose. The purified enzyme was specific towards adenosine. The Michaelis constant was 5.2 X 10(-5) M. The optimum pH was about 7.0 and molecular weight 42000.