Subunit separation in reversed micelle system reveals the existence of active centers both on light and heavy γ-glutamyltransferase subunits

Abstract

Regulation of supra-macromolecular composition and catalytic activity of a heterodimeric enzyme, γ-glutamyltransferase, in the system of Aerosol OT (sodium bis(2-ethylhexyl) sulfosuccinate) reversed micelles in octane were studied. Variation of the surfactant hydration degree (parameter, determining dimensions of the polar inner cavity of the micelle) causes a reversible dissociation of the enzyme to light and heavy subunits. Both enzyme subunits possess catalytic activity. The light and heavy subunits of the enzyme were separated on a preparative scale in a reversed micelle system using ultracentrifugation. The active centers of γ-glutamyltransferase were studied using its irreversible inhibitor — AT-125 (L·(αS.5S)-α-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid). Separation of the γ-glutamyltransferase subunits results in the ‘opening’ of a new active center located at the heavy subunit. In the dimer form of the enzyme this center is masked and it is not accessible to both substrate and inhibitor molecules.