Linked Life Data

9188728

Source:http://linkedlifedata.com/resource/pubmed/id/9188728

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
23
pubmed:dateCreated
1997-7-14
pubmed:abstractText
Initial velocity methods were used to probe the kinetic mechanism of Escherichia coli uridine diphosphate-N-acetylmuramate:L-alanine ligase (UNAM:L-Ala ligase). When the activity (in the forward direction) versus substrate concentration data were plotted in double-reciprocal form, all line patterns were intersecting. The best fit of these data was to the equation for an ordered mechanism with the following parameters: k(cat), 1000 +/- 100 min(-1); Kma, 210 +/- 40 microM; Kmb, 84 +/- 20 microM; Kmc, 70 +/- 15 microM; Kia, 180 +/- 50 microM; Kib, 68 +/- 24 microM. Initial velocity line patterns were also determined when the concentration of one substrate was varied at different fixed concentrations of a second substrate while the third substrate was held at a concentration more than 100 times its Km value. Reciprocal plots of data collected with either ATP or L-alanine present at more than 100 times their Km values resulted in intersecting line patterns. Data collected with UNAM present at 100 times its Km value gave a set of parallel lines. These data are consistent with UNAM binding as the second substrate in an ordered mechanism. ADP, uridine diphosphate-N-acetylmuramoyl-L-alanine (UNAMA), and phosphate were tested as product inhibitors versus substrates. None of the products were competitive inhibitors versus L-alanine or UNAM, while the only observed competitive inhibition was ADP versus ATP. These results are consistent with an ordered kinetic mechanism wherein ATP binds first, UNAM binds second, and ADP is the last product released. Rapid quench experiments were performed in the presence of all three substrates or in the presence of ATP and UNAM. The production of acid-labile phosphate as a function of time is characterized by a burst phase followed by a slower linear phase with the rate close to k(cat) in the presence of all three substrates. Only a burst phase was observed for the time course of the reaction in the presence of ATP and UNAM. In both cases, the burst rate was identical. These observations are consistent with L-alanine being the third substrate to bind in a sequential mechanism involving a putative acyl-phosphate intermediate.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
10
pubmed:volume
36
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
7264-71
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1997
pubmed:articleTitle
Evaluation of the kinetic mechanism of Escherichia coli uridine diphosphate-N-acetylmuramate:L-alanine ligase.
pubmed:affiliation
Department of Macromolecular Biochemistry and Biophysics, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543-4000, USA.
pubmed:publicationType
Journal Article