Alterations in tyrosine aminotransferase isoenzymes of liver of rats as a function of age.

The specific activities (units/mg protein) of tyrosine aminotransferase (TAT) and its isoenzymes, cytoplasmic (c-), mitochondrial (m-) and nuclear (n-TAT), of the liver of 6-, 35- and 76-week old male albino rats were determined. The activities of all the isoenzymes are highest at 6 weeks and are significantly lower at 35 weeks. Total TAT and c-TAT remain unchanged, m-TAT decreases and n-TAT increases significantly after 35 weeks. c-TAT was partially purified from the liver of rats of the three ages to study its kinetic and molecular properties. These properties apparently do not change as a function of age.