Age changes of isoelectric points of the molecular forms of tyrosine aminotransferase from rat liver

Hydrocortisone-induced tyrosine aminotransferase was isolated from liver of young and old rats and purified by ammonium sulfate precipitation, heat treatment, DEAE-cellulose chromatography and isoelectric focusing. Isoelectric points of the molecular forms of the enzyme were as follows: pH 4.30, 5.00, 5.72 for young rats and pH 4.25, 4.7, 6.62 and 8.00 for old rats. At 6 days after the initial homogenization only one major peak in tyrosine aminotransferase activity corresponding to an isoelectric point of pH 5.10 can be recognized.