Journal of Lipid Research, Vol 35, 1441-1451, Copyright © 1994 by Lipid Research, Inc.
Hydrolysis of a novel lysosomotropic enzyme substrate for beta- galactosidase within intact cells
CR Kaneski, SA French, MR Brescia, MJ Harbour and SP Miller
Developmental and Metabolic Neurology Branch, National Institute of Neurological Disordrs and Stroke, National Institutes of Health, Bethesda, MD 20892.
With the goal of improving the detection of lysosomal sphingolipid
hydrolases within intact cells, we have recently synthesized a new
fluorophor, O-[4-(1-imidazolyl)butyl]-2,3-dicyano-1,4-hydroquinonyl
beta-D-galactopyranoside (Im-DCH-beta-Gal). In the present study, we
evaluated the interaction of Im-DCH-beta-Gal and its tetraacetate
derivative, Im-DCH-beta-Gal(OAc)4, with living human fibroblasts. Im-
DCH-beta-Gal was shown to be a specific substrate for human lysosomal
beta-galactosidase in cell homogenates. Im-DCH-beta-Gal(OAc)4 was taken up
and hydrolyzed by normal fibroblasts under physiological culture
conditions. Very little hydrolysis of Im-DCH-beta-Gal(OAc)4 was observed in
fibroblasts genetically deficient in lysosomal acid beta- galactosidase or
in normal cells pretreated with the lysosomal inhibitors chloroquine and
ammonium chloride. Analysis of substrate processing by cells indicated that
normal and acid beta-galactosidase- deficient cells showed similar rates of
uptake and deacetylation of Im- DCH-beta-Gal(OAc)4, with an 80% decrease in
the rate of deglycosylation of substrate by beta-galactosidase-deficient
fibroblasts. However, under our conditions, the fluorescent product was not
well retained by cells. Our results indicate that this novel class of
compounds may be useful in measuring lysosomal enzyme function in intact
cells and may have application as a fluorescent marker for genetically
altered cells.