Five different assay conditions were used to analyse the intracellular proteolytic system of GL. Acid proteinase activity was measured using hide powder azure at pH4 and neutral proteinase activity was measured using hide powder azure and azocasein at pH 8 and two peptide nitroanilides at pH 7. Differences between the activities were apparent from their sensitivity to proteinase inhibitors although all were likely to be due to cysteine proteinases. Indeed all were enhanced by the presence of 1 mM-DTT. The neutral activities could be resolved into at least three forms by ion-exchange chromatography, each form having a different specificity for the substrates used. The acid proteinase activity was similarly separated into different fractions. The intracellular activity of acid proteinase responded differently from that of the neutral activities to culture age or resuspension of cells in fresh medium and starvation buffer. Furthermore, analysis on sucrose density gradients showed that although the neutral activities had a similar subcellular distribution to one another this differed from that of the acid proteinase activity. This suggests that the physiological roles of the acid and neutral proteinases may differ. PAGE using gels containing haemoglobin to detect proteinases was less successful than with other species of protozoa. However, it did reveal multiple forms of acid proteinase.


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