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Cells exposed to horseradish peroxidase (HRP) in their growth medium
take up this enzyme in their phagosomes as phagosomes form. Other
possible entry sites on the cell surface are the endosomes, discharged
trichocyst membrane remnants and the cytoproct (see later). However,
when the cell was exposed for short times a forming phagosome will be
loaded with HRP reaction product that is surrounded with acidosomes
(ac) which are free of HRP reaction product. This shows that
the acidosomes though docked at the early phagosome have not fused
with the early phagosome. Acidosomes acquire HRP quickly if rapid
endocytosis leads to HRP-labeled carrier vesicle formation that are
then transported to and fuse with the acidosomes at the cytopharynx
(not shown). In such a case, acidosomes can contain HRP even while
docked at the early phagosomes, but they acquire the HRP not by
phagocytosis but by endocytosis. po mt, postoral microtubular
bundles. EM taken on 3/23/81 by R. Allen with Hitachi HU11A TEM. Neg.
6,500X. Bar = 1µm. Published in Eur. J. Cell Biol. 29:150-158, 1983.
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