Evidence for a Subcellular Vesicular Site of Collagen Prolyl Hydroxylation

Abstract

Abstract The highest specific activity of prolyl hydroxylase in lung tissue was localized in a particulate fraction which was isolated from tissue homogenates by density gradient centrifugation. Electron microscopic studies showed this fraction to be predominantly vesicles with ribosomes studding their surface. Enzymic hydroxylation by this fraction of exogenous substrate prepared from chick embryos required addition of detergent to the enzyme assay mixture. When hydroxylation was inhibited this subcellular fraction also contained proline-rich, hydroxyproline-deficient substrate which could be hydroxylated in the absence of detergent. These studies indicate a vesicular localization of prolyl hydroxylation and will facilitate future investigations of the intracellular events and regulatory mechanisms involved in collagen synthesis.