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Parathyroid hormone-degrading enzyme of high molecular weight in the cytosol of rat renal cortical cells

Fujita T, Baba H, Sase M, Fukushima M, Nishii Y

Bone and mineral, 1986

Abstract

Using unlabeled bovine parathyroid hormone (b-PTH) as the substrate, the PTH-degrading activity in the 100,000 x g supernatant of rat renal cortex was examined. The PTH-degrading activity showed the highest peak at pH 7.25, along with 3 minor peaks at pH 4.5, 6.0 and 8.5. The neutral PTH-degrading activity of the 100,000 x g supernatant (pH 7.25) was eluted at V0 in Sephadex G-200 gel filtration corresponding to a high molecular weight. The neutral PTH-degrading activity was inhibited by ATP and calcium, but the acid PTH-degrading activity (pH 4.5) was slightly activated by ATP and was uninfluenced by calcium. The cytosolic neutral PTH-degrading activity was not inhibited by PMSF, trypsin inhibitor, E-64, chymostatin, leupeptin or pepstatin, whereas the acid PTH-degrading activity was inhibited by pepstatin, leupeptin, trypsin inhibitor and chymostatin. The neutral and acid PTH-degrading activities most probably depend on different enzymes. The neutral PTH-degrading enzyme is unlike any of the PTH-degrading enzymes so far reported.

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