Subcellular fractionation of human intestinal mucosa by large-scale zonal centrifugation. Localization of the lysophospholipase activity in distal ileum.
The subcellular localization of lysophospholipase activity (EC 3.1.1.5) in human ileal mucosa was studied by rate-zonal and isopycnic density-gradient centrifugation. The subcellular organelles (brush borders, basolateral membranes, lysosomes, mitochondria, and endoplasmic reticulum) were fractionated on a continuous sucrose gradient and located by assay of marker enzymes. Most lysophospholipase activity was found in the brush-border membranes, although the enzyme appeared in basolateral membranes as well. The possible physiological implications of this finding are discussed in view of that lysolecithin can impair the mucosal barrier function in the distal part of ileum. The localization of lysophospholipase to the brush-border membrane could thus serve a favourable purpose, preventing an accumulation of lysolecithin that might facilitate the absorption of potentially antigenic and toxic compounds.