Dynamics of four rat liver plasma membrane proteins and polymeric IgA receptor. Rates of synthesis and selective loss into the bile

L. J. Scott, A. L. Hubbard

Research output: Contribution to journalArticle

Abstract

We have determined the half-lives and amounts per hepatocyte of the polymeric IgA receptor (pIgA-R) and four rat hepatocyte plasma membrane proteins and subsequently have predicted their rates of synthesis and possible routes of degradation. Using in vivo pulse-chase metabolic labeling with L-[35S]cysteine, we found that the pIgA-R had an apparent half-life of 1.1 h. Additional metabolic labeling experiments showed that CE9, HA4, and HA321 had apparent half-lives of 4-5 days, and dipeptidyl peptidase IV had an apparent half-life of 9 days. To quantify the amount of each protein per hepatocyte, homogenates and a standard curve of purified protein were compared by immunoblotting. We found that these proteins were present at 1-8 x 106 molecules/hepatocyte. The calculated rate of synthesis for pIgA-R was 1.6 x 106 molecules/hepatocyte/h, whereas the others were synthesized at much lower rates (0.9-5 x 104 molecules/hepatocyte/h). Using immunoblot analysis, we found that pIgA-R was released into bile at a rate of 30%/h (700%/day), whereas dipeptidyl peptidase IV and HA4 were released at a rate of 2-3%/day. While the majority of the loss of pIgA-R from hepatocytes occurred by release into the bile, less than 30% of the degradation of dipeptidyl peptidase IV and HA4 could be accounted for by this pathway, suggesting that the remaining molecules must be retrieved from the apical surface before degradation.

Original languageEnglish (US)
Pages (from-to)6099-6106
Number of pages8
JournalJournal of Biological Chemistry
Volume267
Issue number9
StatePublished - Jan 1 1992

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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