Chemical modification and amino terminal sequence of calotropin DI from Calotropis gigantea |
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| Institution: | 1. Department of Psychiatry, Morsani College of Medicine, University of South Florida, Tampa, FL, United States;2. James A. Haley Veteran''s Administration Hospital, Tampa, FL, United States;3. Center for Translational Research on Neurological Diseases, The First Affiliated Hospital, Dalian Medical University, Dalian, China;4. Center for Aging & Brain Repair, Department of Neurosurgery & Brain Repair, Morsani College of Medicine, University of South Florida, Tampa, FL, United States;5. Neuroimmunology Laboratory, Department of Psychiatry, Morsani College of Medicine, University of South Florida, Tampa, FL, United States;6. Departments of Biomedical Sciences and Pathology, Saitama Medical Center and Saitama Medical University, Kawagoe, Saitama, Japan;1. Department of Physiology, Xiangya School of Medicine, Central South University, Changsha, Hunan, China;2. Department of Physiology, Medical College of Jishou University, Jishou, Hunan, China |
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| Abstract: | The effect of chemical modification of histidine, lysine, arginine, tryptophan and methionine residues on the enzymatic activity of calotropin DI has been studied. 1,3-Dibromoacetone inhibited the enzyme completely, indicating that a single histidine residue and a cysteine residue are involved in its catalytic activity. Its second bistidine residue was modified with diethyl pyrocarbonate without loss of activity. Modification of seven of its 13 lysine residues with 2,4,6-trinitrobenzene sulphonic acid led to 90% loss of its activity, but no single lysine residue appears to be essential for its activity. Four of the 12 arginine residues by 1,2-cyclohexanedione can be modified with little loss of activity. Modification of a single tryptophan residue and two methionine residues did not inhibit enzymatic activity. The blocked amino-terminal amino acid residue of calotropin DI has been identified as pyroglutamic acid. Its amino-terminal amino acid sequence to residue 14 has been determined and compared with that of papain. They show an extensive homology in their amino-terminal amino acid sequences. |
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