title: In vitro alleviation of heavy metal-induced enzyme inhibition by proline.
abstract: Accumulation of proline in response to toxic heavy metal exposure seems to be wide-spread among plants. To elucidate the role for proline in plant responses to heavy metal stress, we studied the effect of proline on Cd-induced and Zn-induced inhibition of glucose-6-phosphate dehydrogenase (G-6-PDH; EC 1.1.1.49) and nitrate reductase (NR; EC 1.6.6.2) in vitro. Proline appeared to protect both enzymes against Zn and, though less effectively, against Cd. Measurements with a Cd(2+)-specific electrode strongly suggested that this protection was based on a reduction of the free metal ion activity in the assay buffer, due to the formation of metal-proline complexes. There were no indications of any significant role for proline-water or proline-protein interactions. The significance of these findings with regard to heavy metal-induced proline accumulation in vivo is discussed.
authors.affiliation: Department of Ecology and Ecotoxicology, Faculty of Biology, Vrije Universiteit, De Boelelaan 1087, 1081 HV, Amsterdam, The Netherlands
authors.forename: Shanti S.
authors.initials: SS
authors.lastname: Sharma
authors.forename: Henk
authors.initials: H
authors.lastname: Schat
authors.forename: Riet
authors.initials: R
authors.lastname: Vooijs