Subunit interactions of transcarboxylase as studied by circular dichroism

A change in the secondary structure of transcarboxylase from quaternary interactions is monitored by circular dichroism spectroscopy. The change is traced to interactions among the six polypeptides that make up the 12SH subunit. It is fully reversible and is not a result of the conditions used to dissociate the enzyme. Our new method of analyzing circular dichroism spectra for secondary structure works well for this enzyme and its subunits. Even the odd circular dichroism of the 1.3SE subunit analyzes well. There is an increase of 19% in alpha helix and a concomitant decrease of 8% in antiparallel beta sheet and 7% in random structure on association to form the hexameric 12SH subunit.