Properties of Magnesium Chelatase in Greening Etioplasts

Abstract

Evidence was obtained by means of low temperature spectrofluorimetry and high pressure liquid chromatography for the exclusive chelation of Mg2+ into protoporphyrin IX by a plastid preparation extracted from greening cucumber cotyledons. Under the experimental conditions which were optimized for Mg2+ chelation, Zn2+ chelation was not detected. However, Zn2+ chelation was observed when ATP was omitted and ZnCl2 was added to the incubation mixture. The observed Zn2+ chelation was partially nonenzymic. The requirements for the enzyme, Mg chelatase, are discussed in terms of the regulatory function of this enzyme.