title: Cadmium accumulation in the chloroplast of Euglena gracilis.
abstract: Intracellular distribution of Cd, cysteine, glutathione, and Cd-induced thiol peptides in Euglena gracilis cultured under photoheterotrophic conditions was studied. After 3 days of culture with 0.2 mM CdCl2, 62% of the Cd accumulated by cells was equally distributed between the cytosolic and chloroplastic fractions. However, after 8 days, metal content increased in the crude chloroplastic fraction to 40% of total and decreased to 19% in the cytosol; in Percoll-purified chloroplasts the estimated content of Cd raised to 62%. Accumulation of Cd in chloroplasts could be mediated by a transporter of free Cd2+, since uptake of added CdCl2 in isolated chloroplasts exhibited a hyperbolic type of kinetics with a Km of 57 &mgr;M and Vmax of 3.7 nmol (mg protein)-1 min-1. The contents of cysteine and glutathione markedly increased in both chloroplasts (7-19 times) and cytosol (4-9 times) by exposure to Cd2+, although they were always higher in the cytosol. Thiol-containing peptides induced by Cd were mainly located in the cytosol after 3 days, and in the chloroplasts after 8 days of culture. The data suggested that Cd was compartmentalized into chloroplasts in a process that may involve the transport of free Cd and the participation of thiol-peptides.
authors.affiliation: Departamento de Bioquimica, Instituto Nacional de Cardiologia, D.F. 14080, Mexico Departamento de Bioquimica, Facultad de Quimica, UNAM, D.F. 04510, Mexico.
authors.forename: David
authors.initials: D
authors.lastname: Mendoza-Cozatl
authors.forename: Silvia
authors.initials: S
authors.lastname: Devars
authors.forename: Herminia
authors.initials: H
authors.lastname: Loza-Tavera
authors.forename: Rafael
authors.initials: R
authors.lastname: Moreno-Sánchez