A new model for proton pumping in animal cells: the role of pyrophosphate.
The H+-PPase activity was characterized in membrane fractions of ovary and eggs of Rhodnius prolixus. This activity is totally dependent on Mg2+, independent of K+ and strongly inhibited by NaF, IDP and Ca2+. The membrane proteins of eggs were analyzed by western blot using antibodies to the H+-PPase from Arabidopsis thaliana. The immunostain was associated with a single 65-kDa polypeptide. This polypeptide was immunolocalized in yolk granule membranes by optical and transmission electron microscopy. We describe the acidification of yolk granules in the presence of PPi and ATP. This acidification is inhibited in the presence of NAF, Ca2+ and antibodies against H+-PPase. These data show for the first time in animal cells that acidification of yolk granules involves an H+-PPase as well as H+-ATPase.
Motta
L S
LS
Instituto de Biofisica Carlos Chagas Filho, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária-Ilha do Fundão, 21.941-590 Rio de Janeiro, RJ, Brazil.
da Silva
W S
WS
Oliveira
D M P
DM
de Souza
W
W
Machado
E A
EA
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000201:enzymology; D011756:Diphosphates / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism; D005260:Female; D043564:Inorganic Pyrophosphatase / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D009865:Oocytes / Q000201:enzymology; D010053:Ovary / Q000201:enzymology; D010063:Ovum / Q000201:enzymology; D017494:Proton Pumps / Q000378:metabolism*; D012239:Rhodnius / Q000201:enzymology*
D011756:Diphosphates; D004527:Egg Proteins; D008565:Membrane Proteins; D017494:Proton Pumps; D000255:Adenosine Triphosphate; D043564:Inorganic Pyrophosphatase