Purification and Properties of Rat Liver Tyrosine Aminotransferase

A procedure is presented for the purification of l-tyrosine-2-oxoglutarate aminotransferase from the livers of rats previously treated with the synthetic glucocorticosteroid, triamcinolone (9α-fluoro-16α-hydroxyprednisolone diacetate). A 2500-fold purification over crude liver extract was obtained. The final preparation, which appeared to be over 95% homogeneous by ultracentrifugal and electrophoretic criteria, has twice the specific activity of the most active fraction previously reported. The purified enzyme showed three enzymically active components when examined by acrylamide gel electrophoresis. The major component (approximately 95% of the total protein applied to the gel) migrated more rapidly than the two minor components which appeared to be aggregates of the principal component. The purified enzyme which sediments as a single boundary with an s020,w of 5.3 in the ultra-centrifuge has a molecular weight of 115,000 calculated from sedimentation equilibrium studies. The amino acid composition was determined. The enzyme binds approximately 4 moles of pyridoxal 5'-phosphate per 115,000 g of protein but no cortisol binding was detected.