Different oligomeric states are involved in the allosteric behavior of uracil phosphoribosyltransferase from Escherichia coli.
Eur J Biochem
; 240(3): 637-45, 1996 Sep 15.
Article
em En
| MEDLINE
| ID: mdl-8856065
ABSTRACT
Uracil phosphoribosyltransferase, catalyzing the formation of UMP and pyrophosphate from uracil and 5-phosphoribosyl-alpha-1-diphosphate (PPRibP), was purified from an overproducing strain of Escherichia coli. GTP was shown to activate the enzyme by reducing K(m) for PPRibP by about fivefold without affecting Vmax. When started by addition of enzyme, the reactions accelerated over an extended period of time, while enzyme solutions incubated first with GTP and PPRibP displayed constant velocities. This indicated that PPRibP and GTP influenced the structure of the enzyme. Gel-filtration and sedimentation analyses showed that the apparent oligomeric state of uracil phosphoribosyltransferase is defined by a dynamic equilibrium between a slowly sedimenting form (dimeric or trimeric) that has only a little activity, and a more highly aggregated form (pentameric or hexameric), which is more active. It appears that the smaller form predominates in the absence of substrates, while the larger form predominates in the presence of GTP and PPRibP. Guanosine-3',5'-bis(diphosphate) was found to activate the enzyme much like GTP.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Pentosiltransferases
/
Escherichia coli
Idioma:
En
Revista:
Eur J Biochem
Ano de publicação:
1996
Tipo de documento:
Article
País de afiliação:
Dinamarca