ArticleRadiation inactivation of galactose oxidase, a monomeric enzyme with a stable free radical |
| Ellis S. Kempner 1 *, James W. Whittaker 2, Jay H. Miller 1 |
1Laboratory of Physical Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892
2Department of Science and Engineering, School of Medicine, Oregon Health and Sciences University, Beaverton, Oregon 97006
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| email: Ellis S. Kempner (eskempner@yahoo.com) |
*Correspondence to Ellis S. Kempner, Laboratory of Physical Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892
Funded by:
NIH; Grant Number: GM046749
Intramural Research Program of NIAMS
| galactose oxidase radiation target sizes enzymatic activity surviving monomers |
| To determine the radiation sensitivity of galactose oxidase, a 68 kDa monomeric enzyme containing a mononuclear copper ion coordinated with an unusually stable cysteinyl-tyrosine (Cys-Tyr) protein free radical. Both active enzyme and reversibly rendered inactive enzyme were irradiated in the frozen state with high-energy electrons. Surviving polypeptides and surviving enzyme activity were analyzed by radiation target theory giving the radiation sensitive mass for each property. In both active and inactive forms, protein monomer integrity was lost with a single radiation interaction anywhere in the polypeptide, but enzymatic activity was more resistant, yielding target sizes considerably smaller than that of the monomer. These results suggest that the structure of galactose oxidase must make its catalytic activity unusually robust, permitting the enzymatic properties to survive in molecules following cleavage of the polymer chain. Radiation target size for loss of monomers yielded the mass of monomers indicating a polypeptide chain cleavage after a radiation interaction anywhere in the monomer. Loss of enzymatic activity yielded a much smaller mass indicating a robust structure in which catalytic activity could be expressed in cleaved polypeptides. |
Received: 7 September 2009; Revised: 19 November 2009; Accepted: 23 November 2009
10.1002/pro.302
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