Source:http://linkedlifedata.com/resource/pubmed/id/16653187
Switch to
| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
4
|
| pubmed:dateCreated |
2010-6-29
|
| pubmed:abstractText |
The H(+)-translocating inorganic pyrophosphatase (H(+)-PPase) associated with vesicles of the vacuolar membrane (tonoplast) isolated from beet (Beta vulgaris L.) is subject to direct inhibition by Ca(2+) and a number of other divalent cations (Co(2+), Mn(2+), Zn(2+)). By contrast, the H(+)-translocating ATPase (H(+)-ATPase) located on the same membrane is insensitive to Ca(2+). Here we examine the mechanism and feasibility of regulation of the vacuolar H(+)-PPase by cytosolic free Ca(2+) under the conditions thought to prevail in vivo with respect to Mg(2+), inorganic pyrophosphate (PPi), and pH. The minimal reaction scheme that satisfactorily describes the effects of elevated Ca(2+) or CaPPi on the enzyme is one that invokes equilibrium binding of substrate (Mg(2)PPi) at one site, inhibitory binding of Mg(2)PPi to a lower-affinity second site, binding of activator (Mg(2+)) at a third site, and direct binding of Ca(2+) or CaPPi to a fourth site. Changes in enzyme activity in response to selective manipulation of either Ca(2+) or CaPPi are explicable only if Ca(2+), rather than CaPPi, is the inhibitory ligand. This conclusion is supported by the finding that CaPPi fails to mimic substrate in protection of the enzyme from inhibition by N-ethylmaleimide. Furthermore, the reaction scheme quantitatively and independently predicts the observed noncompetitive effects of free Ca(2+) on the substrate concentration dependence of H(+)-PPase activity. The results are discussed in relation to the previous proposal that CaPPi is the principal inhibitory ligand of the vacuolar H(+)-PPase (M. Maeshima [1991] Eur J Biochem 196: 11-17) and the possibility that in vivo modulation of cytosolic free Ca(2+) might constitute a specific mechanism for selective regulation of this enzyme, and consequently for stabilization of PPi levels in the cytoplasm of plant cells.
|
| pubmed:commentsCorrections |
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-16453861,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-16653186,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-16664026,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-16665276,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-16667022,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-1847114,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-1848180,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2351660,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2531142,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2536740,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2543362,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2549870,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-2555340,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-4344648,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-6125388,
http://linkedlifedata.com/resource/pubmed/commentcorrection/16653187-6625165
|
| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:status |
PubMed-not-MEDLINE
|
| pubmed:month |
Dec
|
| pubmed:issn |
0032-0889
|
| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:volume |
100
|
| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
1706-15
|
| pubmed:dateRevised |
2010-9-15
|
| pubmed:year |
1992
|
| pubmed:articleTitle |
Regulation of vacuolar h-pyrophosphatase by free calcium : a reaction kinetic analysis.
|
| pubmed:affiliation |
Biochemistry and Physiology Department, Agricultural and Food Research Council Institute of Arable Crops Research, Rothamsted Experimental Station, Harpenden, Hertfordshire AL5 2JQ, United Kingdom.
|
| pubmed:publicationType |
Journal Article
|