A Simplified Procedure for the Purification of Rat Liver Tyrosine Aminotransferase

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Abstract
Rat liver tyrosine aminotransferase was purified by chromatography on CM-Sephadex C-50 and DEAE-cellulose, (NH4)2SO4 fractionation and gel filtration on Sephadex G-200. Rat livers (400) can be easily worked up by this procedure. This purification method has the advantage that hepatic tryptophan 2,3-dioxygenase, which, like tyrosine aminotransferase, is induced by glucocorticosteroids, can be purified from the same homogenate. Tyrosine aminotransferase purified by this method was specific for 2-oxoglutarate. Its subunits have a MW of 45,000. The following apparent Km were determined L-tyrosine, 1.7 .times. 10-3 M; 2-oxoglutarate, 5.9 .times. 10-4 M; and pyridoxal 5''-phosphate, 2.1 .times. 10-6 M. Tyrosine aminotransferase, depleted of its cofactors, binds 4 molecules of pyridoxal 5''-phosphate per 90,000 daltons with a KA of 2.2 .times. 105 M-1.