Jm. Rodriguezparis et al., CHARACTERIZATION OF LYSOSOMES ISOLATED FROM DICTYOSTELIUM-DISCOIDEUM BY MAGNETIC FRACTIONATION, The Journal of biological chemistry, 268(12), 1993, pp. 9110-9116
Superparamagnetic particles were prepared with iron oxide cores of con
gruent-to 8 nm diameter and dextran coats. After feeding the probe to
the amoeba, Dictyostelium discoideum, for 15 min and chasing for 15 mi
n, a lysosome fraction was isolated magnetically. Isolates contained 7
6% of ingested iron, 82% of ingested fluorescent dextran, 1.3% of cell
protein, 4% of the lipid, 28% of acid phosphatase, and 5% of the vacu
olar H+-ATPase. Enrichment in endocytic markers was congruent-to 60-fo
ld; markers for other organelles were <0.5%. The lysosomes were homoge
neous, round (0.4-1.1 mum in diameter), and frequently adherent to one
another through zones of intimate apposition. Cells were also fed the
iron probe continuously for 3 h to fill their entire endocytic pathwa
y; in this case, isolates contained 3.3% of cell protein, 11% of lipid
, and 49% of cell acid phosphatase. Bis(monoacylglycerol)phosphate (BM
P), a lipid characteristic of lysosomes in animal cells, comprised con
gruent-to 6% of biosynthetically labelled cell lipids and up to half o
f the lipid in the endocytic pathway. Essentially all of the cellular
BMP was recovered in isolates prepared after 3 h of feeding. The speci
ficity and abundance of BMP in the endocytic organelles of this early
diverged protist suggests that this phospholipid serves a universal an
d essential function in endocytosis.