An analysis of intracellular proteinases from antibiotic-producing cells of Penicillium urticae

Two distinct patterns of activity obtained with the substrates azocasein and azocollagen suggested that Penicillium urticae produces at least two intracellular proteinases during its antibiotic-production phase. Cell extracts fractionated using high resolution gel filtration actually separated three major activities. These three pooled fractions contained predominantly cysteine-type proteinases, as indicated by their sensitivities to inhibitors and by the enhancement of their activities with dithiothreitol and ethylenediamine-tetracetic acid. One of these fractions also appeared to contain significant levels of serine-type proteinases. The three pools could be differentiated from one another by changes in their substrate specificities over a range of pH values, and by their stabilities during storage and at elevated temperatures. Further purification by non-denaturing polyacrylamide gel electrophoresis, revealed that two of the fractions each contained five apparently different activities while in the third pooled fraction, thirteen individual activities were detected. The range of properties displayed by these proteinases is consistent with their probable involvement in general protein degradation, a crucial process which during starvation sustains the supply of substrate necessary for secondary enzyme synthesis as well as contributing to the short lifetime of these same secondary enzymes.