Linked Life Data

6721853

Source:http://linkedlifedata.com/resource/pubmed/id/6721853

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
1
pubmed:dateCreated
1984-6-18
pubmed:abstractText
The enzyme-[14C] carboxybiotin complex of sheep liver pyruvate carboxylase was isolated and the reaction between this and pyruvate was studied by using the quenched-flow rapid-reaction technique. At 0.5 degrees C the reaction was 80% complete within 180 ms. The reaction was monophasic and obeyed pseudo-first-order kinetics. Increasing concentrations of Mg2+ caused a decrease in the magnitude of the observed pseudo-first-order rate constant. Throughout the carboxylation of pyruvate, the rate-limiting step of the reaction occurred after the dissociation of carboxybiotin from the first sub-site, whereas in the slow phase of the reaction with 2-oxobutyrate this dissociation is the rate-limiting step. It is possible, from the reaction scheme proposed, that the inhibition of overall enzymic activity by high concentrations of Mg2+ could be caused by the transfer of the carboxy group from biotin to pyruvate becoming rate-limiting. The efficacy of a substrate as a signal for the movement of carboxybiotin from the first sub-site is reflected by the amount that the effective affinity of the enzyme- carboxybiotin complex for Mg2+ is lowered. In the presence of the substrates tested, the affinities of the carboxybiotin complex can be arranged in order of increasing magnitude, i.e.: (formula; see text). The kinetics of the decay of the enzyme-[14C] carboxybiotin complex at 0 degree C in the absence of substrates are similar to the reaction with pyruvate except that the carboxybiotin is also unstable in the first sub-site, to some degree. This similarity allows for the proposal of a general scheme for the decarboxylation of the enzyme- carboxybiotin complex in the presence or in the absence of substrates.
pubmed:commentsCorrections
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Apr
pubmed:issn
0264-6021
pubmed:author
pubmed:issnType
Print
pubmed:day
1
pubmed:volume
219
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
243-51
pubmed:dateRevised
2009-11-18
pubmed:meshHeading
pubmed:year
1984
pubmed:articleTitle
The carboxybiotin complex of pyruvate carboxylase. A kinetic analysis of the effects of Mg2+ ions on its stability and on its reaction with pyruvate.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't