Biosynthesis of type IV and V (alpha A-alpha B) collagens by human placenta.

The collagenous proteins synthesized by placenta in organ culture were characterized. Types I and III collagen accounted for about two-thirds of the collagenous protein produced by the tissue while type IV procollagen comprised around 10%. Type IV collagen contained two chains of 185,000 and 175,000 daltons which are genetically distinct from one another as determined by a peptide mapping procedure. The type IV procollagen was identical to that produced by other tissues based on ratios of 3- to 4-hydroxyproline and hydroxyproline to proline, and on the pattern produced upon polyacrylamide gel electrophoresis before and after peptide mapping procedures. About 20% of the collagen resembled type V collagen in the proportions of 3- and 4-hydroxyproline to proline and of hydroxylysine to lysine, in solubility, and in peptide maps. However, it contained disulfide linked chains larger than those found in the type V collagen solubilized by pepsin. Following pepsin treatment, the disulfide bonds were removed and the mobility of the chains of the labeled protein resembled those in type V collagen. It is likely that the disulfide linked protein represents the intact type V collagen molecule.