1H-NMR relaxometric study of pancreatic serine (pro)enzyme inhibition by a Gd(III) chelate bearing boronic functionalities

Abstract

Binding of the paramagnetic N,N'-bis(m-boroxyphenylcarbamoylmethyl)- diethylenetriamine-N,N',N'-triacetic acid Gd(III) complex (GdBB) to chymotrypsin, chymotrypsinogen, trypsin, typsinogen and pancreatic elastase has been investigated by 1H-NMR relaxometry, between pH 6.0 and 8.5, at 25.0°C. Values of Ki for the competitive inhibition of serine proteinases by GdBB are in excellent agreement with values of Kd obtained by 1H-NMR relaxometry, suggesting that the substrate and the paramagnetic complex bind to the same region. Moreover, 1H-NMR relaxometry allowed to determine values of Kd for GdBB binding to chymotrypsinogen and trypsinogen, both devoid of catalytic activity. The increase of the water proton relaxation rate upon GdBB binding to serine (pro)enzymes may be useful in the design of novel functional contrast agents for magnetic resonance imaging.