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Title: Characterization of the dimer-monomer equilibrium of the papaya Cu/Zn superoxide dismutase and its equilibrium shift by a single amino acid mutation.
Authors: Chi-Tsai Lin;Ti-Jung Kuo;Jei-Fu Shaw;Ming-Ching Kao
Contributors: 國立臺灣海洋大學:生命科學系
Date: 1999
Issue Date: 2018-03-27T07:59:28Z
Publisher: Journal of Agricultural and Food Chemistry
Abstract: Abstract: The coding region of the copper/zinc superoxide dismutase (Cu/Zn SOD) cDNA from papaya fruit, Carica papaya L. cv. Tainong 2, was cloned into an expression vector, pET-20b(+). The Cu/Zn SOD was expressed in Escherichia coli and purified by His-tag technique. Two active forms of the enzyme (30% dimer and 70% monomer) in equilibrium were observed. The activity of the dimeric enzyme was higher than that of the monomeric form. The thermal inactivation rate constant Kd values calculated for the dimer and monomer at 90 °C were −0.0203 and −0.0216 min-1, and the half-lives for inactivation were 41.9 and 31.8 min, respectively. This indicated that the dimeric enzyme was more stable than its monomeric form. The dimerization of the enzyme was inhibited under acidic pH (below 3.0) or imidazole buffer (above 0.5 M), whereas it was not affected under alkaline pH (above 9.0). Both activity and forms of the enzyme were not affected by 1−4% SDS. Furthermore, the dimeric enzyme was much more resistant to proteolytic attack after 3 h of incubation at 37 °C with trypsin or chymotrpsin. In addition, mutation of the papaya Cu/Zn SOD at position 48 from Leu to Phe (L48F) affected the association of monomer, whereas a mutant with Lys substitution (L48K) at the same position tended to dissociate into monomeric form.
Relation: 47(7)
URI: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/45589
Appears in Collections:[Department of Life Science] Periodical Articles

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