The Sequestration and Deposition Mechanism of Cadmium in Fission Yeast

• Main Authors: Lin, Shyh-Mirn, 林士民
• Other Authors: Rong-Huay Juang
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/44100558741803299994

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.