Copper binding studies of lipases from different sources using image binding: mechanism of free copper and chelated copper.

Immobilized metal-ion affinity gel electrophoresis (IMAGE) has been demonstrated to be an efficient tool to study the binding of proteins to chelated transition metals such as Cu(II). IMAGE was exploited to isolate several lipases from different sources and so evaluate their affinities for iminodiacetic acid (IDA)-Cu(II) and, in particular, to evaluate their enzymatic activities while retained on a gel (IMAGE) containing chelated copper [IDA-Cu(II)]. It was found that all lipases can be active within the gel while being coordinated to IDA-Cu(II). It is concluded that active site histidine (most likely) is not involved in the metal recognition and thus other resident histidines serve as electron donors. This is mainly attributed to the known phenomenon of occlusion of the catalytic site by more or less rigid lid structures. The involvement of active site histidine in hydrogen bonding is also evoked.