Proton-pyrophosphatase and polyphosphate in acidocalcisome-like vesicles from oocytes and eggs of periplaneta americana
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Abstract
9 p. : il.Acidocalcisomes are acidic organelles containing large amounts of polyphosphate (poly P), a number of
cations, and a variety of cation pumps in their limiting membrane. The vacuolar proton-pyrophosphatase
(V-Hþ-PPase), a unique electrogenic proton-pump that couples pyrophosphate (PPi) hydrolysis to the
active transport of protons across membranes, is commonly present in membranes of acidocalcisomes. In
the course of insect oogenesis, a large amount of yolk protein is incorporated by the oocytes and stored in
organelles called yolk granules (YGs). During embryogenesis, the content of these granules is degraded
by acid hydrolases. These enzymes are activated by the acidification of the YG by a mechanism that is
mediated by proton-pumps present in their membranes. In this work, we describe an Hþ-PPase activity
in membrane fractions of oocytes and eggs of the domestic cockroach Periplaneta americana. The enzyme
activity was optimum at pH around 7.0, and was dependent on Mg2þ and inhibited by NaF, as well as by
IDP and Ca2þ. Immunolocalization of the yolk preparation using antibodies against a conserved sequence
of V-Hþ-PPases showed labeling of small vesicles, which also showed the presence of high concentrations
of phosphorus, calcium and other elements, as revealed by electron probe X-ray microanalysis. In
addition, poly P content was detected in ovaries and eggs and localized inside the yolk granules and the
small vesicles. Altogether, our results provide evidence that numerous small vesicles of the eggs of
P. americana present acidocalcisome-like characteristics. In addition, the possible role of these organelles
during embryogenesis of this insect is discussed