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Titolo:
UNIDIRECTIONAL TRANSPORT OF ORTHOPHOSPHATE ACROSS THE ENVELOPE OF ISOLATED CAULIFLOWER-BUD AMYLOPLASTS
Autore:
NEUHAUS HE; MAASS U;
Indirizzi:
UNIV OSNABRUCK,FACHBEREICH BIOL CHEM,POSTFACH 4469,BARBARASTR 11 D-49069 OSNABRUCK GERMANY
Titolo Testata:
Planta
fascicolo: 4, volume: 198, anno: 1996,
pagine: 542 - 548
SICI:
0032-0935(1996)198:4<542:UTOOAT>2.0.ZU;2-4
Fonte:
ISI
Lingua:
ENG
Soggetto:
PEA ROOT PLASTIDS; STARCH BIOSYNTHESIS; GLUCOSE PYROPHOSPHORYLASE; SPINACH-CHLOROPLASTS; INORGANIC-PHOSPHATE; INNER MEMBRANE; ADP-GLUCOSE; GLUCOSE-6-PHOSPHATE; TRANSLOCATOR; 3-PHOSPHOGLYCERATE;
Keywords:
AMYLOPLASTS; BRASSICA; GLUCOSE 6-PHOSPHATE TRANSLOCATOR; ORTHOPHOSPHATE TRANSPORT; STARCH SYNTHESIS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
33
Recensione:
Indirizzi per estratti:
Citazione:
H.E. Neuhaus e U. Maass, "UNIDIRECTIONAL TRANSPORT OF ORTHOPHOSPHATE ACROSS THE ENVELOPE OF ISOLATED CAULIFLOWER-BUD AMYLOPLASTS", Planta, 198(4), 1996, pp. 542-548

Abstract

Isolated amyloplasts from cauliflower (Brassica oleracea L. var botrytis) buds are able to export orthophosphate unidirectionally into the incubation medium. This orthophosphate transport appears to be protein-mediated, as indicated by the following observations: (i) low temperature and the presence of inhibitors of protein-mediated transport reduced the rate of orthophosphate export, and (ii) the rate of orthophosphate export became saturated with rising internal substrate concentrations. Micromolar concentrations of 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid inhibited the rate of unidirectional orthophosphate export, thus indicating the involvement of the amyloplastic glucose-6-phosphate (Glc6P)translocator in the unidirectional export of orthophosphate. The effect of rising concentrations of orthophosphate upon the activity of ADP glucose pyrophosphorylase in desalted extracts was determined. Orthophosphate given in concentrations similar to those measured in the amyloplastic stroma under conditions of steady-state rates of Glc6P-dependent starch synthesis inhibited the activity of ADP-glucose pyrophosphorylase significantly. However, even under strong limiting substrate conditions the residual activity was sufficient to catalyze the flux of carbon into starch. The maximal rates of orthophosphate transport (in the counter-exchange mode) by isolated spinach (Spinaciaoleracea L.) chloroplasts and by isolated cauliflower-bud amyloplastswere also determined. These rates were compared with the maximal rates of undirectional orthophosphate export by these plastids. From thesemeasurements we can conclude that, compared with spinach chloroplasts, isolated amyloplasts of cauliflower exhibit a fivefold greater ratioof unidirectional orthophosphate transport to maximal rate of orthophosphate transport in the counter-exchange mode compared to spinach chloroplasts. The determined rate of maximal unidirectional orthophosphate export is sufficient to catalyze the release of additional inorganicphosphate liberated in the amyloplastic stroma during the process of Glc6P-dependent starch synthesis.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 30/03/20 alle ore 09:02:49