Purification and properties of the thermostable acid protease of Penicillium duponti

S EmiG A Iacobucci


An acid protease produced by the thermophilic fungus Penicillium duponti K 1014 has been purified by consecutive ion-exchange and gel permeation chromatography, and crystallized from aqueous acetone solution. The purified endopeptidase gave a symmetrical schlieren peak by sedimentation velocity, and was found to be homogeneous upon disc gel electrophoresis at pH 9.5. The enzyme was most active at pH 2.5 against milk casein and showed high thermostability. An isoelectric point of 3.81 was found by isoelectric focusing. A minimum molecular weight of 41 590 was calculated from the amino acid composition, adopting an arginine content of one residue per mole of enzyme. This minimum molecular weight is in good agreement with the value of 41 000 previously found by gel permeation (Hashimoto, H., Iwaasa, T., and Yokotsuka, T. (1973), Appl. Microbiol. 25, 578). Besides the thermostability, the purified P. duponti protease differs from other well-characterized acid proteases in that it contains carbohydrate, 4.33% expressed as glucose. The enzyme was not affected by p-bromophenacyl bromide, but was completely inactivated by alpha-diazo-p-bromoacetophenone, diazoacetyl-DL-norleucine methyl ester, and diazoacetylglycine ethyl ester, in the...Continue Reading


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