Partial purification and characterization of dipeptidyl-aminopeptidase III fromDictyostelium discoideum

Two types of novel dipeptidyl aminopeptidases from Pseudomonas sp. strain WO24

Two kinds of dipeptidyl aminopeptidase I (DAP I [cathepsin C])-like activities which hydrolyze Gly-Phe-p-nitroanilide (Gly-Phe-pNA) were detected in Pseudomonas sp. strain WO24. They were purified and characterized. The isolated enzymes, named DAP BII and DAP BIII, were revealed to be homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing. DAP BII was estimated to have a molecular mass of 150,000 Da by gel filtration and a subunit size of 73,000 Da by SDS-PAGE, indicating it to be a homodimer. The molecular mass of DAP BIII was evaluated to be approximately 60,000 Da by gel filtration and 69,000 Da by SDS-PAGE, indicating that it is monomeric. The isoelectric points of DAP BII and DAP BIII were 6.1 and 5.0, and their optimal pHs were 8.0 and 8.5 to 9.0, respectively. The result of peptide mapping for DAP BII and DAP BIII showed that these enzymes consist of different components. Both enzymes were completely inhibited by diisopropylphosphofluoride but not by general thiol inhibitors, indicating that they are serine proteases. DAP BII and DAP BIII hydrolyzed Gly-Phe-pNA but not Gly-Arg-pNA, both of which are model substrates for mammalian DAP I. Despite these shared activities toward DAP I, DAP BII released dipeptides from Ala-Ala-pNA and Lys-Ala-4-methylcoumarinamide (a substrate for DAP II), whereas DAP BIII did not hydrolyze either of these compounds and was presumed to prefer substrates composed of bulky, hydrophobic amino acids at P1 and P1' positions. In addition, DAP BII showed no endopeptidase activity, whereas DAP BIII possessed the activity on N-terminally blocked peptide derivatives besides exopeptidase activity. Assays performed with bioactive peptides such as angiotensin I and neuromedin N as substrates indicate that DAP BII has a considerably broader substrate specificity than DAP BIII and is able to hydrolyze an X-Pro bond, an imido bond that few peptidases and no known DAPs can cleave. These characteristics, namely, substrate specificities, molecular mass, pI, peptide mapping, pH optimum, and effect of inhibitors, suggested that the two DAPs purified in this work are distinct enzymes and do not belong to any of the previously reported DAP classes.

The isolation and some properties of dipeptidyl peptidases II and III from porcine spleen

1. Dipeptidyl peptidases (DPP) II and III from porcine spleen have been purified to homogeneity as assessed by disc gel electrophoresis, HPLC and chromatofocusing. 2. The enzyme are both inhibited by diisopropylfluorophosphate suggesting that the active site contains an essential serine residue, but they are also inhibited by a variety of other reagents. 3. The pI of DPP II is 4.8, that of DPP III, 4.0. 4. The former enzyme has a molecular weight of 97,000, the latter 66,000 and both are glycoproteins. 5. The enzymes are compared with those from other sources.

Regulation of cysteine proteinases during different pathways of differentiation in cellular slime molds

Cysteine proteinase activities have been determined using gelatin-SDS-PAGE analysis and assays based on peptide nitroanilides. Vegetative myxamoebae of all species examined contain high levels of cysteine proteinase activity present in multiple forms. In both Dictyostelium discoideum and Polysphondylium pallidum the proteinase content is dependent on whether the cells are grown axenically or in association with bacteria. In all instances development is accompanied by a decreased intracellular cysteine proteinase activity. This occurs during the formation of fruiting bodies in D. discoideum, microcysts in P. pallidum, and macrocysts in Dictyostelium mucoroides. Significant quantities of proteinase activity are always secreted by myxamoebae immediately on starvation. In D. mucoroides this leads to an almost total depletion of intracellular cysteine proteinases by the aggregation stage. As a consequence of this depletion it has been relatively easy to detect a developmentally regulated accumulation of cysteine proteinases at the enzyme activity level, something which has not yet proved possible with D. discoideum. Three cysteine proteinases are produced as D. mucoroides macrocysts develop and mature. In the case of microcyst formation in P. pallidum the proteinase contents of the developing cells and of the microcysts are dependent on how the myxamoebae are grown. In this developmental pathway at least, there is no absolute requirement for specific proteinases to be present (or absent) at a particular stage. The diversity of cysteine proteinases found in cellular slime molds and the variety of features apparent in their regulation suggest that they will prove to be very useful for investigating features of the structure/function relationships in this important group of enzymes.