Polarography as a tool in peptide and protein analysis: studies on metal-chelating substances induced by cadmium in the algae Pheodactylum tricornutum and the graminae Agrostis capillaris.

Methods to determine characteristics and quantities of metal-binding substances are needed in order to identify phytochemical systems for use in agriculture and waste treatment. A metal-binding polypeptide (phytochelatin) was prepared by liquid chromatography from the algae Pheodactylum tricornutum and roots of the graminae Agrostis capillaris after exposure to cadmium. Polarographic (voltammetric) analysis indicated binding of cadmium by the polypeptide at different stabilities. No catalytic hydrogen peak at -1.7 V appeared in the polarogram of plant and algae metal-binding substance, but did appear in the polarogram of the metal-chelating protein metallothionein. In all polarograms, two significant peaks were detected. One at approximately -520 mV probably represents the reduction of single cadmium-sulfur bonds, and one at -930 mV the reduction of cadmium-thiolate complexes. A dose-response relationship between cadmium concentration and peak current at -930 mV was observed after exposure of roots of Agrostis at 5 and 10 microM.