Journal of Applied Physiology, Vol 47, Issue 1 72-78, Copyright © 1979 by American Physiological Society
Protein metabolism in lung: use of isolated perfused lung to study protein degradation
M. J. Chiang, P. Whitney Jr and D. Massaro
This study investigates the use of the isolated perfused lung to study
protein degradation. Proteins were labeled in vivo for 10 min or for 5 h
using L-[U-14C]phenylalanine. When prelabeled lungs were perfused in vitro
virtually all of the acid-soluble and acid-insoluble radioactivity in the
tissue and perfusate remained as phenylalanine. Protein degradation was
measured as the accumulation of free [14C]phenylalanine in ther perfusate;
during the time this accumulated the amount of intracellular free
phenylalanine and the free phenylalanine space remained constant. Proteins
labeled during 10 min had a constant rate of degradation between 45 and 90
min of perfusion (about 11%.h-1); those labeled during 5 h had a constant
rate of degradation for 90 (about 3%.h-1). The percent dry lung weight did
not change during the perfusion. We conclude that measurable rates of
proteolysis of "rapid" and "slowly" turning over proteins can be obtained
while the lung is virtually free of edema. This system should allow studies
on the modulation of proteolysis in intact lung under defined conditions.
