Purification and Characterization of Aspartic Protease Derived from Sf9 Insect Cells

  • GOTOH Takeshi
    Department of Engineering in Applied Chemistry, Graduate School of Engineering and Resource Science, Akita University
  • ONO Hiroki
    Department of Materials-Process Engineering and Applied Chemistry for Environments, Akita University
  • KIKUCHI Ken-Ichi
    Department of Engineering in Applied Chemistry, Graduate School of Engineering and Resource Science, Akita University
  • NIRASAWA Satoru
    Japan International Research Center for Agricultural Sciences
  • TAKAHASHI Saori
    Akita Research Institute of Food and Brewing

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Description

An aspartic protease that is significantly produced by baculovirus-infected Spodoptera frugiperda Sf9 insect cells was purified to homogeneity from a growth medium. To monitor aspartic protease activity, an internally quenched fluoresce (IQF) substrate specific to cathepsin D was used. The purified aspartic protease showed a single protein band on SDS–PAGE with an apparent molecular mass of 40 kDa. The N-terminal amino acid sequence of the enzyme had a high homology to a Bombyx mori aspartic protease. The enzyme showed greatest affinity for the IQF substrate at pH 3.0 with a Km of 0.85 μM. The kcat and kcatKm values were 13 s−1 and 15 s−1 μM−1 respectively. Pepstatin A proved to be a potent competitive inhibitor with inhibitor constant, Ki, of 25 pM.

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