Abstract
Chicken and rat liver xanthine dehydrogenases have similarity in their molecular weights and composition of cofactors. But rat enzyme is known to be convertible from NAD-dependent to O2-dependent type, while chicken enzyme is not convertible easily, In order to know the structural differences between rat and chicken enzymes, limited digestion of both enzymes with protease and chemical modification of NAD-binding site of both enzymes were carried out. Chicken enzyme was modified with 5′-FSBA with the stoichiometry of one mole per mole of enzyme bound FAD and the modified residue was identified to be a tyrosine. Limited digestion of chicken enzyme with subtilisin produced 81 k, 32 k and 20 k dalton of main peptides, and the 14C-FSBA modified residue was found to be located in 32 k dalton. After further digestion of C-FSBA modified peptide with V8 protease, 14C-FSBA peptide of 14 amino acids was obtained and sequenced. On the other hand, rat enzyme was modified with 5′-FSBA with the stoichiometry of 1.5 moles per mole of enzyme bound FAD. Compared to chicken enzyme, the modified enzyme was not reactivated by DTT, suggesting that the modified residue is a lysine. The acid hydrolysate of modified enzyme contained two kinds of modified amino acid residues, CBS-lysine and CBS-tyrosine. The limited digestion of rat enzyme with subtilisin yielded three main peptides of 89 k, 44 k and 19 k dalton. When 14C-FSBA modified enzyme was digested with protease, radioactivity was incorporated into 89 k and 44 k peptides.
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Nishino, T., Nishino, T. & Tsushima, K. 98 STRUCTURES OF XANTHINE DEHYDROGENASES FROM CHICKEN AND RAT LIVERS. Pediatr Res 24, 127 (1988). https://doi.org/10.1203/00006450-198807000-00122
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DOI: https://doi.org/10.1203/00006450-198807000-00122