Open AccessProtein Degradation in the Plasma Membrane of Regenerating Liver and Morris Hepatomas
Author(s) -
TAUBER Rudolf,
REUTTER Werner
Publication year - 1978
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1978.tb12065.x
Subject(s) - chemistry , methionine , membrane , leucine , liver regeneration , protein degradation , biochemistry , blood proteins , membrane protein , medicine , endocrinology , biology , regeneration (biology) , microbiology and biotechnology , amino acid
Protein degradation was investigated in three different states of differentiation: (a) in normal liver, (b) in regenerating liver, and (c) in the Morris hepatomas 7777, 3924A and 9121. Rate constants of degradation ( k d ) and half‐lives ( t 1/2 ) of protein were determined in the plasma membrane, the soluble fraction and in total cell homogenate by use of three different tracers, l ‐[1‐ 14 C]leucine, l ‐[ 35 S]methionine and sodium [ 14 C]carbonate. 1. In regenerating liver the decay of protein‐bound radioactivity was reduced in all fractions investigated. By use of [ 14 C]carbonate the apparent values for the rates of degradation ( k d ) of plasma membrane proteins were: regenerating liver 0.25 ± 0.01, control 0.41 ± 0.01; for the soluble fraction: regenerating liver 0.11 ± 0.01, control 0.31 ± 0.02. No loss of protein‐bound radioactivity could be measured within five days after partial hepatectomy when l ‐[1‐ 14 C]leucine or l ‐[ 35 S]‐methionine was administered. 2. Autoradiographic analysis of the decay of radioactivity in plasma membrane polypeptides indicated that the substantially decreased breakdown of proteins is not restricted to single polypeptides of the plasma membrane. No significant differences in the relative degradation rates of individual plasma membrane proteins from regenerating liver could be found. In normal liver, however, distinct differences were observed. 3. In Morris hepatomas half‐lives varied with age and type of the tumor. In the hepatoma 3924A degradation was decreased substantially, whereas in the more rapidly growing hepatoma 7777 no significant change of the half‐lives could be found. As to the hepatoma 9121, 20 days after inoculation protein catabolism was slightly elevated, but was lowered when determined in 27‐day‐old tumors. 4. From these results it can be concluded that the prolongation of the half‐life of plasma membrane proteins is a characteristic feature of regenerating liver. It is likely that in Morris hepatomas 7777, 9121 and 3924A the regulation of the degradation of these membrane constituents is impaired.