Linked Life Data

9748347

Source:http://linkedlifedata.com/resource/pubmed/id/9748347

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
38
pubmed:dateCreated
1998-10-22
pubmed:abstractText
The vesicular acetylcholine transporter (VAChT) mediates ACh storage in synaptic vesicles by exchanging cytoplasmic ACh with vesicular protons. This study sought to determine the stoichiometry of exchange by analysis of ligand binding and transport kinetics. The effects of different pH values inside and outside, external ACh concentrations, and electrical potential gradients on ACh transport by vesicles isolated from the electric organ of Torpedo were determined using a pH-jump protocol. The equilibrium binding of a high-affinity analogue of ACh is inhibited by protonation with a pKa of 7.4 +/- 0.3. A two-proton model fits the transport data much better than a one-proton model does, and uptake increases at more positive internal electrical potential, as expected for the two-proton model. Thus, the results support the two-proton model. The transport cycle begins with binding of external ACh to outwardly oriented site 2 (KACho = 20 mM) and protonation of inwardly oriented site 1 (pKa1 = 4.73 +/- 0.05). Loaded VAChT reorients quickly (73 000 min-1) and releases ACh to the inside (KAChi = 44 000 mM) and the proton to the outside. Unloaded, internally oriented site 2 binds a proton (pKa2 = 7.0), after which VAChT reorients (150 +/- 20 min-1) in the rate-limiting step and releases the proton to the outside to complete the cycle. Rate constants for the reverse direction also were estimated. Two protons provide a thermodynamic driving force beyond that utilized in vivo, which suggests that vesicular filling is regulated. Other phenomena related to VAChT, namely the time required to fill synaptic vesicles, the fractional orientation of the ACh binding site toward cytoplasm, orientational lifetimes, and the rate of nonquantal release of ACh from cholinergic nerve terminals, were computer-simulated, and the results are compared with physiological observations.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Sep
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
22
pubmed:volume
37
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
13400-10
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed-meshheading:9748347-Acetylcholine, pubmed-meshheading:9748347-Animals, pubmed-meshheading:9748347-Biological Transport, pubmed-meshheading:9748347-Carrier Proteins, pubmed-meshheading:9748347-Cell Fractionation, pubmed-meshheading:9748347-Electric Organ, pubmed-meshheading:9748347-Hydrogen-Ion Concentration, pubmed-meshheading:9748347-Kinetics, pubmed-meshheading:9748347-Membrane Potentials, pubmed-meshheading:9748347-Membrane Transport Proteins, pubmed-meshheading:9748347-Osmolar Concentration, pubmed-meshheading:9748347-Protons, pubmed-meshheading:9748347-Regression Analysis, pubmed-meshheading:9748347-Synaptic Vesicles, pubmed-meshheading:9748347-Time Factors, pubmed-meshheading:9748347-Torpedo, pubmed-meshheading:9748347-Tritium, pubmed-meshheading:9748347-Vesicular Acetylcholine Transport Proteins, pubmed-meshheading:9748347-Vesicular Transport Proteins
pubmed:year
1998
pubmed:articleTitle
Kinetic parameters for the vesicular acetylcholine transporter: two protons are exchanged for one acetylcholine.
pubmed:affiliation
Department of Chemistry, Program in Biochemistry and Molecular Biology, University of California, Santa Barbara 93106, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't