Switch to
Predicate | Object |
---|---|
rdf:type | |
lifeskim:mentions | |
pubmed:issue |
2
|
pubmed:dateCreated |
1986-1-30
|
pubmed:abstractText |
Acinetobacter calcoaceticus belongs to a large phylogenetic cluster of gram-negative procaryotes that all utilize a bifunctional P-protein (chorismate mutase-prephenate dehydratase) [EC 5.4.99.5-4.2.1.51] for phenylalanine biosynthesis. These two enzyme activities from Ac. calcoaceticus were inseparable by gel-filtration or DEAE-cellulose chromatography. The molecular weight of the P-protein in the absence of effectors was 65,000. In the presence of L-tyrosine (dehydratase activator) or L-phenylalanine (inhibitor of both P-protein activities), the molecular weight increased to 122,000. Maximal activation (23-fold) of prephenate dehydratase was achieved at 0.85 mM L-tyrosine. Under these conditions, dehydratase activity exhibited a hysteretic response to increasing protein concentration. Substrate saturation curves for prephenate dehydratase were hyperbolic at L-tyrosine concentrations sufficient to give maximal activation (yielding a Km,app of 0.52 mM for prephenate), whereas at lower L-tyrosine concentrations the curves were sigmoidal. Dehydratase activity was inhibited by L-phenylalanine, and exhibited cooperative interactions for inhibitor binding. A Hill plot yielded an n' value of 3.1. Double-reciprocal plots of substrate saturation data obtained in the presence of L-phenylalanine indicated cooperative interactions for prephenate in the presence of inhibitor. The n values obtained were 1.4 and 3.0 in the absence or presence of 0.3 mM L-phenylalanine, respectively. The hysteretic response of chorismate mutase activity to increasing enzyme concentration was less dramatic than that of prephenate dehydratase. A Km,app for chorismate of 0.63 mM was obtained. L-Tyrosine did not affect chorismate mutase activity, but mutase activity was inhibited both by L-phenylalanine and by prephenate. Interpretations are given about the physiological significance of the overall pattern of allosteric control of the P-protein, and the relationship between this control and the effector-induced molecular-weight transitions. The properties of the P-protein in Acinetobacter are considered within the context of the ubiquity of the P-protein within the phylogenetic cluster to which this genus belongs.
|
pubmed:grant | |
pubmed:language |
eng
|
pubmed:journal | |
pubmed:citationSubset |
IM
|
pubmed:chemical | |
pubmed:status |
MEDLINE
|
pubmed:month |
Dec
|
pubmed:issn |
0003-9861
|
pubmed:author | |
pubmed:issnType |
Print
|
pubmed:volume |
243
|
pubmed:owner |
NLM
|
pubmed:authorsComplete |
Y
|
pubmed:pagination |
470-9
|
pubmed:dateRevised |
2007-11-14
|
pubmed:meshHeading |
pubmed-meshheading:4083897-Acinetobacter,
pubmed-meshheading:4083897-Allosteric Regulation,
pubmed-meshheading:4083897-Chromatography, DEAE-Cellulose,
pubmed-meshheading:4083897-Chromatography, Gel,
pubmed-meshheading:4083897-Enzyme Activation,
pubmed-meshheading:4083897-Hydro-Lyases,
pubmed-meshheading:4083897-Kinetics,
pubmed-meshheading:4083897-Molecular Weight,
pubmed-meshheading:4083897-Phenylalanine,
pubmed-meshheading:4083897-Prephenate Dehydratase,
pubmed-meshheading:4083897-Tyrosine
|
pubmed:year |
1985
|
pubmed:articleTitle |
Interconvertible molecular-weight forms of the bifunctional chorismate mutase-prephenate dehydratase from Acinetobacter calcoaceticus.
|
pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, P.H.S.,
Research Support, U.S. Gov't, Non-P.H.S.
|