RG: Collagen in the human lung. Quantitation of rates of synthesis and partial characterization of composition

fundamental in normal lung structure and function. Methods have been developed to examine human fetal and adult lung collagen with respect to its composition and synthesis. The second trimester fetal lung has a large number of cells per unit lung mass (36.6±2.7 lsg DNA/mg dry wt) and relatively small amounts of col-lagen (17.0±5.3 Ag collagen/mg dry wt). The number of cells per unit lung mass in the adult lung (11.1±3.4 Ag DNA/mg dry wt) is 30 % of the number of cells in the fetal lung, but the adult has 11 times more collagen (196±25 Ag collagen/mg dry wt). The composition of fetal lung collagen can be par-tially characterized by extraction with salt at neutral pH, acetic acid, or guanidine. The extracted chains, representing 10 % of the total lung collagen, chromato-graph as al and a2 chains, each with a mol wt of 100,000 and an animo acid composition characteristic for collagen but not specific for lung. Short-term explant cultures of fetal and adult lung synthesize a chains which can be isolated by ion-ex-change chromatography. These chains, representing 30-40 % of the total collagen synthesized by the explants, coelectrophorese with extracted collagen chains on acrylamide gels; they are destroyed by clostridial col-lagenase and they have a mol wt of 100,000. Although the composition of the collagen synthesized by these explants can be only partially characterized, the rate of synthesis of both collagen and noncollagen protein can be quantitated. In fetal lung, 4.0±1.2 % of the amino acids incorporated into protein per hour ar