Regulation of the synthesis of tyrosine aminotransferase: the relationship to mRNATAT

The activity of the hepatic enzyme tyrosine aminotransferase (TAT) is the sum of many diverse regulatory factors. These include the developmental stage of the animal, the hormonal and nutritional environment of the animal (or tissue culture cell), other extrinsic and intrinsic regulatory cycles and factors (including cytoplasmic substances), and chromatin structure. Although TAT is subject to a number of post-translational modifications, alterations in catalytic activity always parallel changes in enzyme amount. In a few instances this is due to a selective change in TAT degradation, but most are due to changes in the rate of aminotransferase synthesis. Recent studies have shown that TAT synthesis is generally directly correlated with the activity, and presumably amount, of the mRNA that codes for tyrosine aminotransferase.