| Summary: | 碩士 === 國立臺灣大學 === 農業化學系研究所 === 86 === Schizosaccharomyces pombe 806與Schizosaccharomyces pombe ATCC 2476這
兩種裂殖性酵母菌在環境中含有較高鎘濃度時，能維持生長而不至死亡。追
究其原因：S. pombe 806是利用 (g-Glu-Cys)n-Gly, (n = 2 ~ 4)，一般簡稱植物
螯合素 (phytochelatin, PC) 與重金屬鎘進行結合，以便隔絕並避免細胞受重
金屬的毒害，然而S. pombe ATCC 2476的耐鎘機制經本實驗室分析發現，並
無phytochelatin或metallothionein等重金屬結合蛋白質，而是產生一種鎘誘
生性蛋白質，加強了S. pombe ATCC 2476對鎘的耐受程度。當ATCC 2476
在最低限培養基中生長至菌數為107，加入最終濃度為0.1 mM鎘溶液再培
養12 hr收集，其細胞粗抽液經過一連串的純化步驟：膠體過濾層析 Sephadex
G-50)、陰離子交換層析 (DEAE Sephacel)、脫鹽膠體過濾 (Sephadex G-75) 及
FPLC (Superose 12)，再經16.5% Tricine SDS-PAGE可得到近乎均質、分子
量約為12 kD的鎘結合蛋白質。其胺基酸組成經分析發現，酸性胺基酸Asn
及Gln的含量遠高於Cys，故不同於已知的PC或metallothionein之組成，所
以推測此鎘結合蛋白質應是利用羧基 (carboxyl group) 與鎘進行結合。其N-
端胺基酸序列經分析為：V-K-Q-V-X-D-X-X-E-F-K-, 可是經序列比對，並無
相類似者，另外。由實驗結果判斷，RNA也有可能參與鎘與結合蛋白質所
形成的複合物。
Schizosaccharomyces pombe 806 (Sp806) and its variety ATCC 2476 were
resistant to environmental cadmium. Sp806 produced heavy metal binding
substance, phytochelatin (PC), which chelated cadmium ion in the cell. On the
other hand, ATCC 2476 produced neither PC nor metallothioneins. Instead, it
synthesized a cadmium inducible protein that bound cadmium ion very
efficiently. The ATCC 2476 culture was grown in the minimum culture medium
to the cell density of 107/mL, and then the cadmium concentration was added to
0.1 mM. After 12 h cultivation, the cell was harvested and its total protein
extracted. Through purification steps including gel filtration Sephadex G-50,
DEAE ion exchange, Sephadex G-75 desalting, and Superose 12 FPLC, an
apparently homogeneous cadmium binding protein with a molecular weight of
12 kD was obtained on tricine SDS-PAGE. This protein contained very high
percentage of the amino acids Asx and Glx, and very trace amount of Cys was
detected. This implied that this cadmium binding protein was distinct from PC
or metallothionein. The N-terminal amino acid sequence was analyzed as
VKQVXDXXEFK-, and no homologous sequence was found in the protein
database of SWISSPRO at this moment. Non-covalent bound RNA component
was found in this protein, which might play a role in the formation of the
protein-cadmium complex.
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