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Evidence for pyroglutamyl peptidase I and prolyl endopeptidase activities in the rat insulinoma cell line RINm 5F: lack of relationship with TRH metabolism.

Abstract : Thyrotropin-Releasing hormone (TRH)-degrading pyroglutamyl peptidase I (PGP I) and prolylendopeptidase (PE) activities have been demonstrated in rat insulinoma RINm 5F cell line. These two enzymes catalyze the conversion of TRH to Histydyl-Proline-Diketopiperazine and to acid TRH respectively. After cell fractionation, we found all the PGP I and PE activities in the cytosolic fraction. The membrane-bound PGP II activity is not detectable in the RINm 5F cells. Further investigations on these two cytosolic enzymes show that pyroglutamyl- and proline-containing peptides are inhibitors of each TRH-degrading enzyme. Gel filtration chromatography on Sephadex G100 shows that PGP I and PE activity have an apparent molecular mass of about 18 kDa and 57 kDa, respectively. Kinetic analysis with TRH as substrate, gives a Km of 44 microM and 235 microM, and a Vmax of 1.49 and 8.80 pmol/min/micrograms protein for PGP I and PE, respectively. Immunoreactive TRH, His-Pro-Diketopiperazine and acid TRH levels in the cell line extracts are 2.2 +/- 0.9, 22.5 +/- 11.1 and 28.7 +/- 14.6 pg/1O6 cells, respectively. When cells have been incubated for 2 to 72 hours with a P.E. inhibitor (Z-Gly-Pro-CHN2) at 5 x 10(-7) M, both cell PGP I and PE activities are inhibited. No change in the cellular content of immunoreactive TRH, His-Pro-Diketopiperazine and acid TRH have been observed in treated cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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https://hal-amu.archives-ouvertes.fr/hal-01803473
Contributor : l'Houcine Ouafik <>
Submitted on : Wednesday, May 30, 2018 - 1:53:09 PM
Last modification on : Thursday, May 31, 2018 - 1:09:57 AM

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  • HAL Id : hal-01803473, version 1
  • PUBMED : 1681421

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P. Salers, L Ouafik, P. Giraud, A. Dutour, J. Maltese, et al.. Evidence for pyroglutamyl peptidase I and prolyl endopeptidase activities in the rat insulinoma cell line RINm 5F: lack of relationship with TRH metabolism.. Molecular and Cellular Biochemistry, Springer Verlag, 1991, pp.15-24. ⟨hal-01803473⟩

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