Partial Characterization of Collagenous and Noncollagenous Basement Membrane Proteins Synthesized by the 14.5-Day Rat Embryo Parietal Yolk SacIn Vitro

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Abstract
Parietal yolk sacs isolated from 14.5-day rat embryos and incubated in vitro with [14C]proline, [3H]mannose or 3H-labeled amino acid mixture synthesized and secreted basement membrane collagenous and noncollagenous glycoprotein components with relative MW of 350,000 (350 K), 220,000 (220K), 185,000 (185K), 175,000 (175K) and 150,000 (150K). The 185K and 175K components appeared to be similar to the pro[procollagen]-.alpha.(IV) and pro-.alpha.2(IV) chains, respectively, which have been isolated from other sources. These components were completely susceptible to bacterial collagenase but were only partially susceptible to .alpha.-chymotrypsin digestion. The 350K and 220K components appeared to be similar to subunits of laminin (or PYS A and PYS B, respectively) which have been previously characterized, while the 150K component may be similar to entactin (or PYS C). These components were completely resistant to bacterial collagenase and completely susceptible to .alpha.-chymotrypsin digestion. The basement membrane of the parietal yolk sac (Reichert''s membrane) stained intensely with antibodies directed against rat laminin or mouse basement membrane procollagen. The 14.5-day rat embryo parietal yolk sac is a useful system for studying the structure, biosynthesis and deposition of basement membrane components.