L. Jacobsberg, E. Kantrowitz, C. McMurray
Dec 19, 1973
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Influential Citations
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Quality indicators
Journal
Biochemical and biophysical research communications
Abstract
Abstract Tetraiodofluorescein (TIF) increases the activity of aspartate transcarbamylase (ATCase) at a concentration only one one-hundredth that of ATP needed to produce comparable activation. At high concentrations, however, the dye decreases the enzyme's activity. In contrast, the isolated catalytic subunit (C 3 ) is inhibited by TIF at any concentration. These results are interpreted to indicate two classes of dye binding sites on the enzyme:an activating class on the regulatory subunits, perhaps those sites at which the physiological activator ATP binds, and an inhibiting class of sites on the catalytic subunits. A difference absorption spectrum, observed when TIF interacts with ATCase, is modified by ATCase's substrates and effectors. Thus TIF is a potentially valuable optical probe of ATCase conformation.