Dipeptidyl peptidase III of human cataractous lenses. Partial purification

A partial purification of dipeptidyl peptidase III has been achieved from human cataractous lens. The specific activity was increased 45.5-fold over that of the original aqueous extract. The exopeptidase exhibited a marked preference for the release of Arg-Arg from Arg-Arg-2-NNap at the optimum pH 8.8 and 37 degrees. The Km for this substrate was estimated to be 6.061 X 10(-3). Lens DPP III was inhibited by EDTA, p-chloromercuriphenyl sulfonate, puromycin and DFP. The preparation contained leucyl aminopeptidase and a neutral endopeptidase as contaminating proteases.