A vacuolar-type proton pump in a vesicle fraction enriched with potassium transporting plasma membranes from tobacco hornworm midgut
Mg-ATP dependent electrogenic proton transport, monitored with fluorescent acridine orange, 9-aminoacridine, and oxonol V, was investigated in a fraction enriched with potassium transporting goblet cell apical membranes of Manduca sexta larval midgut. Proton transport and the ATPase activity from the goblet cell apical membrane exhibited similar substrate specificity and inhibitor sensitivity. ATP and GTP were far better substrates than UTP, CTP, ADP, and AMP. Azide and vanadate did not inhibit proton transport, whereas 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide were inhibitors. The pH gradient generated by ATP and limiting its hydrolysis was 2-3 pH units. Unlike the ATPase activity, proton transport was not stimulated by KCl. In the presence of 20 mM KCl, a proton gradient could not be developed or was dissipated. Monovalent cations counteracted the proton gradient in an order of efficacy like that for stimulation of the membrane-bound ATPase activity: K+ = Rb+ much greater than Li+ greater than Na+ greater than choline (chloride salts). Like proton transport, the generation of an ATP dependent and azide- and vanadate-insensitive membrane potential (vesicle interior positive) was prevented largely by 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide. Unlike proton transport, the membrane potential was not affected by 20 mM KCl. In the presence of 150 mM choline chloride, the generation of a membrane potential was suppressed, whereas the pH gradient increased 40%, indicating an anion conductance in the vesicle membrane. Altogether, the results led to the following new hypothesis of electrogenic potassium transport in the lepidopteran midgut. A vacuolar-type electrogenic ATPase pumps protons across the apical membrane of the goblet cell, thus energizing electroneutral proton/potassium antiport. The result is a net active and electrogenic potassium flux.
- Research Organization:
- Univ. of Munich (Germany, F.R.)
- OSTI ID:
- 5696240
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 264:19; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ACID ANHYDRASES
ALKALI METALS
ANIMALS
ARTHROPODS
ATP
ATP-ASE
BARYONS
BIOLOGICAL EFFECTS
CATIONS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
DYES
ELEMENTARY PARTICLES
ELEMENTS
ENZYME ACTIVITY
ENZYMES
FERMIONS
HADRONS
HYDROLASES
IMIDES
INSECTS
INVERTEBRATES
IONS
LARVAE
LEPIDOPTERA
LITHIUM
MEMBRANE TRANSPORT
MEMBRANES
METALS
MOTHS
NUCLEONS
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHOHYDROLASES
POTASSIUM
PROTONS
RUBIDIUM
TRANSITION ELEMENTS
VANADIUM