Biochemical studies on dipeptidyl peptidases I to IV of the human placenta

Homogenates of human term placentae were utilized to demonstrate the presence of four dipeptidyl peptidases (DPP I to IV) after sequential fractionations with gel filtration and anion-exchange chromatography. DPP I was assayed with SerTyrNA as substrate and showed the characteristics of a thiol-dependent serine enzyme with optimum at pH 4.5 and a molecular weight of 210,000. DPP II, analysed with LysAlaNA as substrate, had an optimum at pH 5.5 and a molecular weight of 130,000 with no dependence on thiol groups or divalent ions. DPP III was studied with ArgArgNA as substrate. It was optimally hydrolysed at pH 8.8 and had a molecular weight of 84,000. The enzyme was highly suppressed by chelating agents but could be reactivated by Co2+ and some other divalent ions. DPP IV, with GlyProNA as substrate, displayed an optimum at pH 8.2. The fractionations displayed multiple forms of the enzyme, possibly indicating the presence of proto- and polymeric DPP IV activities. The protomer had a molecular weight of 260,000 and showed no dependence on thiol groups but was sensitive to Zn2+.