|
|
||||||||
|
Reversibility of H+-ATPase and H+-Pyrophosphatase in Tonoplast Vesicles from Maize Coleoptiles and Seeds1
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
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ASPB Publications | PLANT PHYSIOLOGY | THE PLANT CELL | |
|---|---|---|---|