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Characterization of a ribosomal inhibitory polypeptide of protein phosphatase-1 from rat liver.
- Source :
-
European Journal of Biochemistry . 7/1/96, Vol. 239 Issue 1, p183-189. 7p. - Publication Year :
- 1996
-
Abstract
- About 4% of the spontaneous phosphorylase phosphatase activity in a rat liver extract was associated with the ribosomal fraction and stemmed from both protein phosphatase- I (PP-1) and protein phosphatase-2A (PP-2A). However. after repeated washings only PP-1 remained bound to the ribosomes. The activity of ribosome-associated PP-1 (PP-1R) was partially latent and could be increased 2-3-fold by incubation with trypsin and an additional 50% by incubation with low concentrations of exogenous type-I catalytic subunit. In contrast, incubation of the ribosomal fraction with MgATP resulted in a 50% drop in the activity of PP-IR. We have purified from a ribosomal extract a basic polypeptide (pI ⩾ 10.5) of 23 kDa that potently inhibited PP-I. This ribosomal inhibitor of PP-I. termed RIPP-1. was at least 30-times less efficient in inhibiting other major Ser/Thr protein phosphatases (PP-2A. PP-2B and PP-2C). RIPP-1 was identified as a non-competitive inhibitor of PP-I with a substrate-dependent potency. The lowest K, (approximately 20 nM) was obtained with phosphorylase and myelin basic protein as substrates. Besides instantaneously inhibiting the type-1 catalytic subunit. RIPP- I also converted the catalytic subunit in a time-dependent manner (t1/2 = 45 mm at 25°C) into a less active conformation. Unlike the inhibition, this slow inactivation was not reversed by the removal of RIPP- 1. We propose that RIPP- I accounts, at least in part. for the latency of PP-IR. [ABSTRACT FROM AUTHOR]
- Subjects :
- *ABDOMEN
*PHOSPHORYLATION
*LIVER
*BILIARY tract
*MICROSOMES
*RIBOSOMES
Subjects
Details
- Language :
- English
- ISSN :
- 00142956
- Volume :
- 239
- Issue :
- 1
- Database :
- Academic Search Index
- Journal :
- European Journal of Biochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 15799748
- Full Text :
- https://doi.org/10.1111/j.1432-1033.1996.0183u.x