Structural differences among procollagens associated with rough and smooth microsomes from chick embryo cartilage.

Epiphyseal cartilages of 12-day chick embryo were labeled in vitro with [%]proline. By subjecting the [“C]proline-labeled tissues to subcellular fractionation, it was possible to obtain radioactive procollagens as they were associated with smooth and rough microsomes. Analyses of the procollagens thus obtained indicated that the components in the rough microsome fraction comprised both singleand triple-stranded forms in nearly equal proportions while those in the smooth microsome fraction were present predominantly as triple-stranded forms. When hydroxylation of procollagen polypeptides was inhibited by 2,2’-dipyridyl, unhydroxylated procollagens accumulated in the rough microsomal fraction as singleand triplestranded forms. Labeling experiments using [“C]glucose revealed a marked difference in the extent of glycosylation among the singleand triple-stranded procollagens in different submicrosomal fractions. Digestion of the procollagen components with bacterial collagenase yielded, in each case, a large glycopeptide fraction characterized by the presence of glucose, galactose, mannose, and N-acetylglucosamine, plus a fraction of small peptides characterized by the presence of glucose and galactose. The characterization and comparison of these glycopeptide fragments further defined the nature of the additional peptide region in the various procollagen components, and, when combined with information derived from studies of [14C]proline-labeled procollagens, supported the view that glycosylation of the additional region is completed in the rough endoplasmic reticulum prior to formation of the triple-stranded form, whereas glucose and galactose continue to be incorporated into the a region after the formation of triple strands and the movement of the triple strands into the Golgi complex.