Substrate Specificity and Kinetic Mechanism of Escherichia coli Ribulokinase
| Autor: | W. W. Cleland, Barbara Gerratana, Lac V. Lee |
|---|---|
| Rok vydání: | 2001 |
| Předmět: |
Magnetic Resonance Spectroscopy
Stereochemistry Pentoses Biophysics Xylitol Ribitol Biochemistry Substrate Specificity chemistry.chemical_compound Adenosine Triphosphate Sugar Alcohols Arabitol Escherichia coli Magnesium Enzyme kinetics Phosphorylation Molecular Biology Xylulose Pentosephosphates Ribulokinase Ribulose Substrate (chemistry) Hydrogen-Ion Concentration Kinetics Phosphotransferases (Alcohol Group Acceptor) Crystallography chemistry |
| Zdroj: | Archives of Biochemistry and Biophysics. 396:219-224 |
| ISSN: | 0003-9861 |
| DOI: | 10.1006/abbi.2001.2613 |
| Popis: | l -Ribulokinase is unusual among kinases since it phosphorylates all four 2-ketopentoses with almost the same kcat values. The Km's differ, however, being 0.14 mM for l - and 0.39 mM for d -ribulose and 3.4 mM for l - and 16 mM for d -xylulose. In addition, l -arabitol is phosphorylated at C-5 (Km 4 mM) and ribitol (adonitol) is phosphorylated to d -ribitol-5-phosphate (Km 5.5 mM), but d -arabitol, xylitol, and aldopentoses are not substrates. The Km's for MgATP depend on the substrates, being 0.02 mM with l -ribulose, 0.027 mM with d -ribulose and l -xylulose, and 0.3–0.5 mM with the other substrates. In the absence of a sugar substrate there is an ATPase with Km of 7 mM and kcat 1% of that with sugar substrates. The initial velocity pattern is intersecting, and MgAMPPNP is competitive vs MgATP and uncompetitive vs l -ribulose. l -Erythrulose is competitive vs l -ribulose and when MgATP concentration is varied induces substrate inhibition which is partial. These data show that the mechanism is random, but there is a high level of synergism in the binding of sugar and MgATP, and the path in which the sugar adds first is strongly preferred. |
| Databáze: | OpenAIRE |
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