Subunit interactions in aspartate transcarbamylase. The interaction between catalytic and regulatory subunits and the effect of ligands

The interaction between the catalytic subunit (c3) and the regulatory subunit (r2) of aspartate transcarbamylase from Escherichia coli was studied by measuring the reversible formation of the c3r6 complex as a function of r2 concentration. Conversion to the native enzyme was prevented by using a very low concentration of c2 (40 ng per ml) in the presence of bovine serum albumin. A simple hyperbolic r2 saturation curve was obtained suggesting …