JBC, Vol. 250, Issue 18, 7332-7342, Sep, 1975
Characterization of cell-free synthesis of collagen by lung polysomes in a heterologous system
J. F. Collins and R. G. Crystal
In normal lung growth, post-pneumonectomy lung growth, and in possibly
several lung disorders, there are marked alterations in the density of
collagen and changes in the rate of synthesis of collagen relative to the
synthesis of other lung proteins. To provide a technology to begin to
understand these changes at the molecular level, polysomes were prepared
from rabbit lung and translated in a heterologous cell-free system
including rabbit reticulocyte 0.5 M KCl ribosomal wash fraction and liver
tRNA. Collagen was shown in the cell-free product by collagenase
sensitivity, hydroxylation of incorporated proline by peptidyl prolyl
hydroxylase, agarose gel chromatography, and sodium dodecyl sulfate
acrylamide gel electrophoresis. The cell-free system was optimized with
respect to K+, Mg2+, amino acids, and ribosomal wash fraction and used
under conditions where total protein synthesis and collagen synthesis are
linear with respect to time and amount of polysomes. Under these
conditions, collagen synthesis was directed almost entirely by polysomes
derived from the endoplasmic reticulum. Polysomes isolated from late fetal
lung directed collagen synthesis at twice the rate (per polysome) as those
polysomes isolated from adult lung. Similar changes were seen if lung tRNA
replaced liver tRNA and if lung ribosomal wash fraction replaced
reticulocyte wash fraction. Although these changes in cell-free lung
collagen synthesis with tissue explants, further studies will have to be
carried out to determine whether, in fact, age-related alterations in
control of lung collagen synthesis are truly explained by these findings.