1. Allantoin racemase is a novel enzyme which catalyzes the conversion of S(+)-and R(minus)-allantoin into the racemate. 2. The enzyme is present in Pseudomonas testosteroni, Pseudomonas putida and five biotypes of Pseudomonas fluorescens, but absent in a number of other Pseudomonas species. 3. The enzyme of Ps. testosteroni was purified 133-fold and exposes optimal activity at pH 8.0-8.2 and 50 degrees C. The enzyme is stable on heating for 15 min at 70 degrees C. 4. The enzyme appeared to be specific for the optical isomers of allantoin and no cofactors are involved in the reaction. 5. The optical aspecificity of allantoinase of Proteus rettgeri was reaffirmed.
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The Structure and Function of a Microbial Allantoin Racemase Reveal the Origin and Conservation of a Catalytic Mechanism.
Biochemistry
November 2016
Department of Life Sciences, University of Parma, Parma, Italy.
The S enantiomer of allantoin is an intermediate of purine degradation in several organisms and the final product of uricolysis in nonhominoid mammals. Bioinformatics indicated that proteins of the Asp/Glu racemase superfamily could be responsible for the allantoin racemase (AllR) activity originally described in Pseudomonas species. In these proteins, a cysteine of the catalytic dyad is substituted with glycine, yet the recombinant enzyme displayed racemization activity with a similar efficiency (k/K ≈ 5 × 10 M s) for the R and S enantiomers of allantoin.
View Article and Find Full Text PDFReaction Mechanism and Catalytic Fingerprint of Allantoin Racemase.
J Phys Chem B
July 2014
École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
The stereospecific oxidative decomposition of urate into allantoin is the core of purine catabolism in many organisms. The spontaneous decomposition of upstream intermediates and the nonenzymatic racemization of allantoin lead to an accumulation of (R)-allantoin, because the enzymes converting allantoin into allantoate are specific for the (S) isomer. The enzyme allantoin racemase catalyzes the reversible conversion between the two allantoin enantiomers, thus ensuring the overall efficiency of the catabolic pathway and preventing allantoin accumulation.
View Article and Find Full Text PDFCharacterization of the structure and function of Klebsiella pneumoniae allantoin racemase.
J Mol Biol
July 2011
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
The oxidative catabolism of uric acid produces 5-hydroxyisourate (HIU), which is further degraded to (S)-allantoin by two enzymes, HIU hydrolase and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase. The intermediates of the latter two reactions, HIU and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline, are unstable in solution and decay nonstereospecifically to allantoin. In addition, nonenzymatic racemization of allantoin has been shown to occur at physiological pH.
View Article and Find Full Text PDFPurine utilization by Klebsiella oxytoca M5al: genes for ring-oxidizing and -opening enzymes.
J Bacteriol
February 2009
Department of Microbiology, University of California, One Shields Ave., Davis, CA 95616-8665, USA.
The enterobacterium Klebsiella oxytoca uses a variety of inorganic and organic nitrogen sources, including purines, nitrogen-rich compounds that are widespread in the biosphere. We have identified a 23-gene cluster that encodes the enzymes for utilizing purines as the sole nitrogen source. Growth and complementation tests with insertion mutants, combined with sequence comparisons, reveal functions for the products of these genes.
View Article and Find Full Text PDFAllantoin racemase was isolated from cells of Candida utilis, and purified by chromatography on columns of DEAE-cellulose and Sephadex G-100. Using this purified enzyme, the racemization of allantoin in deuterium oxide was investigated. Polarimetric and PMR spectroscopic analyses showed that racemization of allantoin by the enzyme proceeded in parrallel with release of the hydrogen atom (5-H) attached to the asymmetric carbon (C-5) of allantoin.
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