630
Biogenesis, Structure and Function of Lysosomes
Tab. 1
Examples of lysosomal storage diseases.
Disease
Enzyme defciency
Stored material
Tay-Sachs
β
-Hexosaminidase
Gangliosides
α
-Mannosidosis
α
-Mannosidase
α
-Mannose oligosaccharides
Sialidosis
Sialidase
Sialyl oligosaccharides
Farber
Ceramidase
Ceramide
Gaucher
Glucocerebrosidase
Glucoceramide
Niemann–Pick
Sphingomyelinase
Sphingomyelin
Hunter
Iduronate sulfatase
Heparin sulfate and dermatan sulfate
Galactosialidosis
Cathepsin A
Galactyl and sialyl oligosaccharides
I-cell
6-Phosphotransferase
Multiple substances
lysosomal membrane, LAMP2a. In addi-
tion, independent of its peptidase activity,
cathepsin A protects two lysosomal glycosi-
dases,
β
-D-galactosidase and
N
-acetyl-
α
-
neuraminidase, from rapid intralysosomal
destruction. In addition, cathepsin A is re-
quired for the proper lysosomal targeting
of
N
-acetyl-
α
-neuraminidase. A defect in
cathepsin A results in a combined deF-
ciency of lysosomal activities of these two
glycosidases and leads to the disease galac-
tosialidosis.
9
Conclusions
Lysosomes are dynamic, multifunctional
organelles. Lysosomal enzymatic content
can be regulated under certain circum-
stances, but most control over the di-
gestion of macromolecules is maintained
by
the
sequestration
of
hydrolytic
en-
zymes into membrane-bound organelles.
Control of substrate delivery to the lyso-
somes appears to be the rate-limited pro-
cess in these proteolytic pathways. Much
less is known about delivery of nucleic
acids
and
lipids
for
lysosomal
degra-
dation, but these topics are worthy of
study.
See also
Developmental Cell Biol-
ogy; Electron Microscopy in Cell
Biology.
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