| Abstract: | 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 K m of 0.85 μM. The k cat and k cat?K m values were 13 s?1 and 15 s?1 μM?1 respectively. Pepstatin A proved to be a potent competitive inhibitor with inhibitor constant, K i, of 25 pM. |
