Interaction of tetraiodofluorescein with a modified form of aspartate transcarbamylase.

Abstract
Low concentrations of the dye tetraiodofluorescein activate native aspartate transcarbamylase (aspartate carbamoyltransferase, carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2), while high concentrations inhibit the enzyme''s activity. This produced similar effects upon a modified form of aspartate transcarbamylase produced by Escherichia coli grown in a culture medium supplemented with thiouracil. The ATP-induced activation is reduced in the modified form of the enzyme to the same extent as is the tetraiodofluorescein-induced activation. Thus, a relationship is demonstrated between the internal mechanisms by which ATP and tetraiodofluorescein activate aspartate transcarbamylase.