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Reversibility of H+-ATPase and
H+-Pyrophosphatase in Tonoplast Vesicles from Maize
Coleoptiles and Seeds1
Arnoldo Rocha Façanha and
Leopoldo de Meis*
Instituto de Ciências Biomédicas, Departamento de
Bioquímica Médica, Universidade Federal do Rio de
Janeiro, Cidade Universitária, RJ-21941-590, Brazil
Tonoplast-enriched vesicles isolated
from maize (Zea mays L.) coleoptiles and seeds
synthesize ATP from ADP and inorganic phosphate (Pi) and inorganic
pyrophosphate from Pi. The synthesis is consistent with reversal of the
catalytic cycle of the H+-ATPase and
H+-pyrophosphatase (PPase) vacuolar membrane-bound enzymes.
This was monitored by measuring the exchange reaction that leads to 32Pi incorporation into ATP or inorganic pyrophosphate. The
reversal reactions of these enzymes were dependent on the proton
gradient formed across the vesicle membrane and were susceptible
to the uncoupler carbonyl cyanide
p(trifluoromethoxy)-phenylhydrazone and the detergent
Triton X-100. Comparison of the two H+ pumps showed that
the H+-ATPase was more active than H+-PPase in
coleoptile tonoplast vesicles, whereas in seed vesicles H+-PPase activity was clearly dominant. These findings may
reflect the physiological significance of these enzymes in different
tissues at different stages of development and/or differentiation.
1
This research was supported by grants from
Programa de Apois ao Desenvolvimento Cientifico e Tecnologico-Conselho
Nacional de Desenvolvimento Científico e Tecnológico,
Financiadora de Estudos e Projetos, and Fundação de Amparo
á Pesquisa do Estado do Rio de Janeiro. A.R.F. is a recipient of
a fellowship from Conselho Nacional de Desenvolvimento
Científico e Tecnológico.
*
Corresponding author; e-mail demeis{at}bioqmed.ufrj.br; fax
55-21-270-8647.
Plant Physiol. (1998) 116: 1487-1495
Copyright Clearance Center: 0032-0889/98/116/1487/09
© 1998 American Society of Plant Physiologists
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