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We found that Notched-fin eelpout, which lives off the north east coast of Japan, expresses an antifreeze protein (AFP). The liver of this fish contains DNAs that encode at least 13 type III AFP isoforms (denoted nfeAFPs). The primary sequences of the nfeAFP isoforms were categor-ized into SP- and QAE-sephadex binding groups, and the latter were fur-ther divided into two subgroups, QAE1 and QAE2 groups. Ice crystals observed in HPLC-pure nfeAFP fractions are bipyramidal in shape with different ratios ofc andaaxes, suggesting that all the isoforms are able to bind ice | iFEBS Journal Co-operative effect of the isoforms of type III antifreeze protein expressed in Notched-fin eelpout Zoarces elongatus Kner Yoshiyuki Nishimiya1 Ryoko Sato1 Manabu Takamichi2 Ai Miura1 and Sakae Tsuda1 2 1 FunctionalProtein Research Group Research Institute of Genome-based Biofactory RIGB National institute of Advanced Industrial Science and Technology AIST Sapporo Japan 2 Division of BiologicalSciences Graduate Schoolof Science Hokkaido University Sapporo Japan Keywords co-operative effect Notched-fin eelpout type III antifreeze protein Correspondence S. Tsuda FunctionalProtein Research Group Research Institute of Genome-based Biofactory RIGB NationalInstitute of Advanced IndustrialScience and Technology AIST 2-17-2-1 Tsukisamu-Higashi Toyohira Sapporo 062-8517 Japan Fax 81 11 857 8983 Tel 81 11 857 8912 E-mail sakae.tsuda@aist.go.jp Note The nucleotide and protein sequences reported here have been deposited in the DDBJ database under the accession numbers AB188389-AB188401. Received 27 August 2004 revised 9 November 2004 accepted 17 November 2004 We found that Notched-fin eelpout which lives off the north east coast of Japan expresses an antifreeze protein AFP . The liver of this fish contains DNAs that encode at least 13 type III AFP isoforms denoted nfeAFPs . The primary sequences of the nfeAFP isoforms were categorized into SP- and QAE-sephadex binding groups and the latter were further divided into two subgroups QAE1 and QAE2 groups. Ice crystals observed in HPLC-pure nfeAFP fractions are bipyramidal in shape with different ratios of c and a axes suggesting that all the isoforms are able to bind ice. We expressed five recombinant isoforms of nfeAFP and analyzed the thermal hysteresis TH activity of each as a function of protein concentration. We also examined the change in activity on mixing the isoforms. TH was estimated to be 0.60 C for the QAE1 isoform 0.11 C for QAE2 and almost zero for the SP isoforms when the concentrations of these .
