Linked Life Data

7733662

Source:http://linkedlifedata.com/resource/pubmed/id/7733662

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
1995-5-26
pubmed:abstractText
We have investigated kinetics of pyrophosphate synthesis and phosphate-water oxygen exchange catalyzed by rat liver cytosolic and mitochondrial pyrophosphatases in the presence of Mg2+ as cofactor. A common kinetic model derived for these reactions implies that they involve formation of enzyme-bound pyrophosphate and proceed through two parallel pathways: pathway I, utilizing two magnesium phosphate molecules, and pathway II, utilizing both magnesium phosphate and free phosphate. Pyrophosphate formation is greatly facilitated in the active sites of both pyrophosphatases ([E.PPi]/[E.2Pi] = 0.11-0.24) compared to solution. The rate constants for PPi binding/release, bound PPi hydrolysis/synthesis, and two Pi binding/release steps catalyzed by cytosolic and mitochondrial pyrophosphatases were enumerated for pathway I. There is no unique rate-limiting step for pathway I for both enzymes in either direction. A modulating effect of magnesium phosphate on the oxygen exchange is observed with the cytosolic pyrophosphatase, explicable in terms of an allosteric phosphate-binding site or random-order release of two phosphate molecules from the active site. A remarkable feature of these mammalian pyrophosphatases versus their microbial counterparts is their high efficiency in pyrophosphate synthesis. The turnover numbers in the direction of synthesis are 14 and 9.3 s-1 for the cytosolic and mitochondrial enzymes, respectively (9 and 16% relative to hydrolysis turnover numbers). The results demonstrate that the enzyme-catalyzed synthesis of pyrophosphate, the simplest high-energy polyphosphate, can proceed at a high rate in the absence of an external energy input, such as that provided by protonmotive force in membrane systems.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0003-9861
pubmed:author
pubmed:issnType
Print
pubmed:day
20
pubmed:volume
318
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
340-8
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1995
pubmed:articleTitle
Rates of elementary steps catalyzed by rat liver cytosolic and mitochondrial inorganic pyrophosphatases in both directions.
pubmed:affiliation
A. N. Belozersky Institute of Physico-Chemical Biology and School of Chemistry, Moscow State University, Russian Federation.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't