Type V collagens of the human placenta: trimer alpha-chain composition, ultrastructural morphology and peptide analysis.

The alpha-chain trimer composition of type V collagen preparations from human placental membrane and villi was determined by two-dimensional electrophoresis on a non-denaturing polyacrylamide gel system followed by electrophoresis in the presence of sodium dodecylsulfate. In preparations isolated from placental membranes pure type V collagen was found with the alpha-chain composition [alpha 1(V)]2 alpha 2(V). In preparations from placental villi two different collagen trimers could be identified with alpha-chain compositions [alpha 1(V)]2 alpha 2(V) and [alpha 3(V)]3. Two-dimensional peptide maps after chymotryptic digestion of the various alpha-chain revealed distinct patterns for alpha 1(V), alpha 2(V) and alpha 3(V) suggesting unique structures for all three alpha-chains. Shadowing of the two collagen preparations with carbon-platinum by the rotary shadowing technique allowed the visualization of the individual molecules. In the placental membrane preparations, a uniform species of molecules was present while in placental villi preparations the same elongated form of collagen was found together with larger aggregates presumably containing molecules with the alpha 3-chain component. These data are interpreted to indicate that so-called type V collagen, at least in preparations from placental villi, contain two distinct collagen molecules.