| Summary: | 碩士 === 台北醫學院 === 醫學研究所 === 89 === Of Amyotrophic Lateral Sclerosis (ALS) , a progressive neurodegenerative disorder cases, 10% are familial and 90% are sporadic. The mutations found in the Cu,Zn-SOD (SOD1) are the causes of 20% of familial ALS. Most mutations cause the decrease of the SOD enzyme activity and some of them are due to the loss of zinc affinity or alteration of the zinc binding site.
Zinc and cadmium constitute group IIB of the periodic table of elements and are uniformly divalent. They share certain common biological responses. In order to investigate the possible causes of heavy metal interactions, we have constructed, expressed, and purified human Cu,Zn-SOD in E. coli with equal amounts of copper and zinc but different concentrations of cadmium in LB broth. First, SDS-PAGE and western blot analysis illustrated a 23kDa monomer. Second, the more cadmium added, the lower enzyme activities remained. Third, by atomic absorption spectrophotometer, we found that the more cadmium added, the more cadmium atoms and the less zinc atoms detected in purified Cu,Zn-SOD.
The results of observation and estimation of the purified Cu,Zn-SOD protein structure from native gel and circular dichroism indicate that the structure of apo-SOD, without any metals, is much different from Cu,Zn-SOD and Cu,Zn-SOD with 500 nM cadmium. Besides, secondary structure of Cu,Zn-SOD with 500 nM cadmium is much close to apo-SOD.
On the other hand, we have confirmed that cadmium is a strong inducer of metallothionein as previous studies reported. These results indicated that cadmium might effect zinc contents of Cu,Zn-SOD owing to its strong induction of metallothioneins which also bind zinc. Therefore, cadmium might play a role in sporadic ALS. These findings may offer some directions to study pathogenic mechanism.
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