| Summary: | 博士 === 國立臺灣大學 === 農業化學系 === 86 === Fission yeast Sp806 produced phytochelatins (PC) when exposed
to heavy metal Cd.
Short PC molecules appeared first at the beginning of Cd
induction, then if the Cd
pressure sustained in the environment, longer PC molecules were synthesized to
chelate Cd and produced a stable Cd-PC complex. This low-molecular-weight Cd-PC
complex (LMW) was transported very quickly into the yeast vacuole, and a high-
molecular-weight form of complex (HMW) was formed. The Cd then might be
transported out of the vacuole, and eventually out of the cell.
When yeast was cultured on the agar plate, and a narrow stripe of filter paper
soaked with high concentration of Cd solution was placed in the middle of the
plate, three types of cell were observed after several days of incubation. The
cell grown on the area nearest to the Cd stripe (area 1) had
white colonies, and
tiny particles were observed on the cell surface by scanning electron
microscopy (SEM). The cell next to it (area 2) produced metal luster, which
contained high amount of Cd and sulfite. The surface of the cell on this area
was stained with spots, which might be formed by the deposition of Cd being
transported out to the cell surface. The farthest area (area 3) grown normally
and had healthy appearance.
PC molecule was not detectable in the collected material from the metal
luster of area 2. Instead a short peptide (H6) which had a very high Cd
binding capacity was purified from it, and the sequence of H6 was deduced
as HHHHHHG(BZ). It was then proposed that H6 might chelate Cd ions by
its imidazole groups on the histidine residues, or by the carboxylic or the
carbonyl groups on its acidic or amidic amino acids. The glycine in between
might serve as a free hinge, and made this Cd-H6 complex a stable and safe
deposit for Cd.
|
|---|
