Post-proline endopeptidase in human placenta.

Post-proline endopeptidase (EC 3.4.21.26) was found in human placenta, purified 3390-fold from it and briefly characterized. The post-proline endopeptidase could be completely separated from dipeptidyl peptidase IV (EC 3.4.14.5) by hydrophobic phenyl-Sepharose chromatography. The pH optimum of the enzyme was 6.7. The Km values for 7-(Succinyl-Gly-Pro)-4- methylcoumarinamide was 1.0 mM. The molecular weight of this enzyme was estimated to be 140 000 by gel filtration and 67 000 by dodecyl sulfate gel electrophoresis, indicating its dimeric structure. Human placental post-proline endopeptidase was suggested to be a thiol proteinase by inhibition studies.